Process for producing resin varnish containing semi-ipn composite, thermosetting resin and, provided using the same, resin varnish for printed wiring board, prepreg and metal-clad laminate

ABSTRACT

A thermosetting resin varnish that includes a thermosetting resin composition of an uncured semi-IPN composite having compatibilized with one another (A) a polyphenylene ether, (B) a butadiene polymer which contains in the molecule thereof 40% or more of a 1,2-butadiene unit having a 1,2-vinyl group in the side chain thereof, and which is not chemically modified, and (C) a crosslinking agent; (D) an inorganic filler; and (E) a saturated thermoplastic elastomer. Also, a resin varnish for a printed circuit board, a prepreg, and a metal-clad laminate, using the thermosetting resin varnish.

This application is a Divisional application of prior application Ser.No. 12/596,165, filed Oct. 16, 2009, the contents of which areincorporated herein by reference in their entirety. No. 12/596,165 is aNational Stage application filed under 35 USC 371, of International(PCT) Application No. PCT/JP2008/058010, filed Apr. 25, 2008.

FIELD OF THE INVENTION

The present invention relates to a process for producing a resin varnishcontaining a thermosetting resin of semi-IPN composite and, a resinvarnish for printed circuit board, a prepreg, and a metal-clad laminateobtained by using the same. More particularly, the present inventionconcerns a process for producing a novel resin varnish for printedcircuit board usable in an electronic device having an operatingfrequency of more than 1 GHz and, a resin varnish for printed circuitboard, a prepreg, and a metal-clad laminate obtained by using theprocess.

BACKGROUND INVENTION

Mobile communication devices including cell phones as representativeexamples and devices for their base stations, network-associatedelectronic devices, such as a server and a router, large-size computers,and the like are demanded to transmit and process a large amount of datawith low loss at a high speed. For transmitting and processing a largeamount of data at a high speed, an electric signal having a highfrequency is needed. However, basically, the higher the frequency, themore likely the electric signal attenuates. That is, the electric signalhaving a higher frequency has properties such that the output is likelyto weaken in a shorter transmission distance to cause large loss.Therefore, for meeting the demands for the above transmission andprocessing of data with low loss at a high speed, the printed circuitboard mounted on the device for transmission and processing of data mustbe improved in its properties to further reduce the transmission loss,particularly, transmission loss in a high frequency band.

For obtaining a printed circuit board having a low transmission loss,substrate materials using a fluororesin having a low relativepermittivity and a low dielectric loss tangent have conventionally beenused. However, the fluororesin generally has a high melt temperature, ahigh melt viscosity, and relatively low flowability, and therefore has aproblem in that high-temperature and high-pressure conditions must beemployed in the pressing for the fluororesin. In addition, thefluororesin also has a problem in that, when applied to the use ofhigh-multilayer printed circuit board for use in the above-mentionedcommunication devices, network-associated electronic devices, large-sizecomputers, and others, the fluororesin is unsatisfactory in theworkability, dimensional stability, and adhesion to the metal plating.

Therefore, as a substitute for the fluororesin, resin materials forprinted circuit board which meet the requirements of the high frequencyapplication are being studied. Of these resin materials, the use ofpolyphenylene ether known as one of the resins having the most excellentdielectric properties among the heat-resistant polymers has attractedattention. However, like the fluororesin, the polyphenylene ether is athermoplastic resin having a high melt temperature and a high meltviscosity. Therefore, when applied to the use of printed circuit board,for lowering the melt temperature and melt viscosity of the resin sothat lower-temperature and lower-pressure conditions can be employed inthe pressing, or for imparting to the resin a heat resistance at themelt temperature of polyphenylene ether (230 to 250° C.) or higher, aresin composition using polyphenylene ether and a thermosetting resin incombination has conventionally been used.

For example, a resin composition using a polyphenylene ether and anepoxy resin in combination (see Patent document 1), a resin compositionusing a polyphenylene ether and a bismaleimide in combination (seePatent document 2), a resin composition using a polyphenylene ether anda cyanate ester in combination (see Patent document 3), a resincomposition using a polyphenylene ether, a styrene-butadiene copolymeror polystyrene, and triallyl cyanurate or triallyl isocyanurate incombination (see Patent documents 4 and 5), a resin composition using apolyphenylene ether and a polybutadiene in combination (see Patentdocuments 6 and 7), a resin composition obtained bypreliminarily-reacting modified polybutadiene having a functional group,such as a hydroxyl group, an epoxy group, a carboxyl group, or a(meth)acryl group, and bismaleimide and/or cyanate ester (see Patentdocument 8), a resin composition using a polyphenylene ether havingadded or grafted thereon a compound having an unsaturated doublebond-containing group and the above triallyl cyanurate, triallylisocyanurate, or polybutadiene in combination (see Patent documents 9and 10), a resin composition using a reaction product of a polyphenyleneether and an unsaturated carboxylic acid or unsaturated acid anhydrideand the above bismaleimide in combination (see Patent document 11), aresin composition using a low molecular-weight (oligomer) typepolyphenylene ether oligomer having an unsaturated doublebond-containing group at the end thereof and polybutadiene or astyrene-butadiene copolymer in combination, and a resin compositionusing the above polyphenylene ether resin composition and an inorganicfiller in combination (see Patent document 12) have been proposed. Thesepatent documents disclose that, for removing the above-mentioneddisadvantages of the thermoplastic resin while maintaining the lowtransmission loss of the polyphenylene ether, it is preferred that thecured resin does not have many polar groups.

-   [Patent Document 1] Japanese Patent Application Laid-Open No.    58-69046-   [Patent Document 2] Japanese Patent Application Laid-Open No.    56-133355-   [Patent Document 3] Japanese Published Examined Application No.    61-18937-   [Patent Document 4] Japanese Patent Application Laid-Open No.    61-286130-   [Patent Document 5] Japanese Patent Application Laid-Open No.    3-275760-   [Patent Document 6] Japanese Patent Application Laid-Open No.    62-148512-   [Patent Document 7] Japanese Patent Application Laid-Open No.    59-193929-   [Patent Document 8] Japanese Patent Application Laid-Open No.    58-164638-   [Patent Document 9] Japanese Patent Application Laid-Open No.    2-208355-   [Patent Document 10] Japanese Patent Application Laid-Open No.    6-184213-   [Patent Document 11] Japanese Patent Application Laid-Open No.    6-179734-   [Patent Document 12] Japanese Patent Application Laid-Open No.    2005-105061

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present inventors have made close studies on the application of theresin composition using polyphenylene ether and a thermosetting resin incombination, representatively described in Patent documents 1 to 12, topossibility for the use of laminate for printed circuit board.

As a result, with respect to the resin composition described in each ofPatent documents 1, 2, and 11, after being cured, the dielectricproperties deteriorated due to the effect of the epoxy resin orbismaleimide which is highly polar, which indicates that the resincomposition is unsuitable for the high frequency application.

With respect to the composition using polyphenylene ether and cyanateester in combination described in Patent document 3, the dielectricproperties were excellent, but the heat resistance was lowered aftermoisture absorption.

With respect to the composition using polyphenylene ether and triallylcyanurate or triallyl isocyanurate in combination described in each ofPatent documents 4, 5, 9, and 10, the relative permittivity was slightlyhigher, and further the dielectric properties tended to remarkably driftdue to moisture absorption.

With respect to the resin composition using polyphenylene ether andpolybutadiene in combination described in each of Patent documents 4 to7 and 10, the dielectric properties were excellent, but there wereproblems in that the resin itself had a low strength and a high thermalexpansion coefficient, which indicates that the resin composition isunsuitable for the application of high-multilayer printed circuit board.

Patent document 8 discloses the resin composition using polyphenyleneether and modified polybutadiene in combination for improving theadhesion to a metal or glass substrate. However, this resin compositionhad a problem in that the dielectric properties markedly deteriorated,particularly in a high frequency band of 1 GHz or more, as compared tothose of a resin composition using unmodified polybutadiene.

With respect to the composition using a reaction product ofpolyphenylene ether and an unsaturated carboxylic acid or unsaturatedacid anhydride described in Patent document 11, due to the effect of theunsaturated carboxylic acid or unsaturated acid anhydride which ishighly polarity, the dielectric properties more markedly deterioratethan those of a composition using general polyphenylene ether.

With respect to the composition using a low molecular-weight (oligomer)type polyphenylene ether oligomer having an unsaturated doublebond-containing group at the end thereof and a thermosetting resin, suchas polybutadiene, in combination described in Patent document 12, thecurable polyphenylene ether oligomer per se has dielectric propertiespoorer than those of not only general polyphenylene ether but also thecured product of polybutadiene homopolymer resin. In other words, inthis composition, excellent dielectric properties inherent in thepolyphenylene ether deteriorate, and therefore the dielectric propertiesof the cured composition are poorer than those of a composition usinggeneral polyphenylene ether. In addition, the curable polyphenyleneether oligomer remarkably increases the cost, as compared to the generalpolyphenylene ether.

It is considered that there is demand for the composition which hassolved the above problems, namely, the thermosetting resin compositioncontaining polyphenylene ether, which has removed the above-mentioneddisadvantages of the thermoplastic resin and which exhibits excellentdielectric properties.

Further, the present inventors have paid attention to the dielectricproperties, particularly the reduction of the transmission loss, andmade studies. As a result, it has been found that only the process ofusing a resin having a low permittivity and a low dielectric losstangent cannot satisfy the requirements of the electric signal having ahigh frequency further increased in recent years. The transmission lossof electric signal is classified into loss caused due to the insulatinglayer (dielectric loss) and loss caused due to the conductor layer(conductor loss), and hence, when a resin having a low permittivity anda low dielectric loss tangent is used, only the dielectric loss isreduced. For further reducing the transmission loss, it is necessary toalso reduce the conductor loss.

As a process for reducing the conductor loss, for example, a process canbe used in which a metal-clad laminate using a metallic foil havingsmall surface roughness on the roughened surface side (hereinafter,referred to as “M side”) corresponding to the bonding surface betweenthe conductor layer and the insulating layer, specifically, a metallicfoil having an M-side surface roughness (ten-point average roughness;Rz) of 5 μm or less (hereinafter, referred to as “low-profile foil”) isemployed.

The present inventors have conducted studies on the use of athermosetting resin having a low permittivity and a low dielectric losstangent as a material for the printed circuit board for use in the highfrequency application and the use of a low-profile foil as a metallicfoil.

As a result of the studies conducted by the present inventors, it hasbeen found that, with respect to the laminate formed using the resincomposition described in each of Patent documents 1 to 12 and alow-profile foil, the adhesion (bonding force) between the insulating(resin) layer and the conductor (metallic foil) layer is too small tosecure the required peeling strength of the metallic foil from theresin. The reason for this is presumed that the polarity of resin is lowand further the anchoring effect of the metallic foil is poor due to thesmall roughness of the M side. Further, in a heat resistance test aftermoisture absorption for the laminate, peeling disadvantageously occurredbetween the resin and the metallic foil. The reason for this is presumedthat the bonding force between the resin and the metallic foil is small.From these results, the present inventors have found that the resincompositions described in Patent documents 1 to 12 have, in addition tothe above-mentioned problems, a problem in that it is difficult to usethe resin composition and a metallic foil having small surfaceroughness, such as a low-profile foil, to form a laminate.

Particularly, the resin system of polyphenylene ether and a butadienehomopolymer posed the following serious problems. These resins areinherently incompatible with each other, and it is difficult to obtain ahomogeneous resin composition from these resins. Therefore, when theresin composition containing these resins is used as such, the resincomposition in an uncured state has a problem of tackiness due to thedrawback of the butadiene homopolymer, making it impossible to obtain aprepreg having smooth appearance and excellent handling properties.Further, when a prepreg produced from such a resin composition and ametallic foil are used to form a metal-clad laminate, the resins arecured in a heterogeneous state (a state of macro phase separation).Therefore, in addition to the problem of external appearance, thereoccurs a decrease in the heat resistance after moisture absorption, andthe defects of the butadiene homopolymer system are more marked, andvarious troubles such as low fracture strength or large thermalexpansion coefficient occurred.

Further, the metallic foil peeling strength is too low to apply alow-profile foil to the metal-clad laminate. Such a low metallic foilpeeling strength is presumed to be caused by the low cohesive failurestrength of the resin near the metallic foil upon peeling rather thanthe low interface bonding force between the butadiene homopolymer andthe metallic foil.

Accordingly, for solving the above problems, it is an object of thepresent invention to provide a process for producing a resin varnishfrom which a printed circuit board can be produced wherein the printedcircuit board has excellent dielectric properties particularly in a highfrequency band and has a small change in the dielectric properties aftermoisture absorption, and can significantly reduce the transmission loss,and exhibits excellent heat resistance after moisture absorption andexcellent thermal expansion properties and satisfies the metallic foilpeeling strength, a resin varnish, a prepreg, and a metal-clad laminateobtained by using the same.

The embodiments of the present invention are not limited to theinvention which solves all the problems accompanying the prior art.

Means to Solve the Problems

Japanese Patent Application No. 2007-116785, which is the basicapplication of the present invention claiming the priority, iscollectively involved in the present specification for all purposes.

The present inventors have conducted extensive and intensive studies onthe resin composition containing a polyphenylene ether with a viewtoward solving the above-mentioned problems accompanying theconventional resin composition. As a result, they have found a novelprocess for producing a resin varnish comprising a polyphenyleneether-modified butadiene polymer which is an uncured semi-IPN compositehaving a novel construction in which a polyphenylene ether and aprepolymer of a chemically unmodified butadiene polymer and acrosslinking agent are compatibilized with each other, an inorganicfiller, and a saturated thermoplastic elastomer, wherein the processcomprises mixing together the inorganic filler and saturatedthermoplastic elastomer and then mixing together the resultant mixtureand the polyphenylene ether-modified butadiene polymer to produce aresin varnish, and a resin varnish produced by the novel and uniqueprocess has been achieved. In addition, it has been found that, whenusing the resin varnish in a printed circuit board, the resultantprinted circuit board has excellent dielectric properties in a highfrequency band and excellent moisture absorption dependency of thedielectric properties, and hence can advantageously reduce thetransmission loss and exhibit excellent heat resistance (particularly,heat resistance after moisture absorption) and low thermal expansionproperties. Further, it has been found that a laminate for printedcircuit board using the resin varnish has high metallic foil peelingstrength and therefore can use therein a metallic foil having smallsurface roughness, particularly a low-profile foil, and the presentinvention has been completed.

Specifically, the present invention is directed to a process forproducing a thermosetting resin varnish containing a thermosetting resincomposition, which contains an uncured semi-IPN composite, an inorganicfiller, and a saturated thermoplastic elastomer, wherein the processcomprises the steps of: preliminary reacting, (B) a butadiene polymerwhich contains in the molecule thereof 40% or more of a 1,2-butadieneunit having a 1,2-vinyl group in the side chain thereof, and which isnot chemically modified and (C) a crosslinking agent, in the presence of(A) a polyphenylene ether to obtain a polyphenylene ether-modifiedbutadiene prepolymer which is an uncured semi-IPN composite; mixingtogether (D) an inorganic filler and (E) a saturated thermoplasticelastomer to obtain a mixture; and mixing together the obtained mixtureand the polyphenylene ether-modified butadiene prepolymer which is anuncured semi-IPN composite.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the step for mixing together themixture and the polyphenylene ether-modified butadiene prepolymer isperformed at a temperature of 60° C. or lower.

The present invention is directed to the process for producing athermosetting resin varnish, wherein, in the step for obtaining apolyphenylene ether-modified butadiene prepolymer, the polyphenyleneether-modified butadiene prepolymer is obtained by preliminary reactingso that a conversion rate of the component (C) becomes in the range offrom 5 to 100%.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the component (C) contains at leastone maleimide compound represented by the following general formula (1):

wherein R₁ is an m-valent aliphatic or aromatic organic group, Xa and Xbmay be the same or different and each is a monovalent atom or organicgroup selected from a hydrogen atom, a halogen atom, and an aliphaticorganic group, and m represents an integer of 1 or more.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the component (C) is at least onemaleimide compound selected from the group consisting ofN-phenylmaleimide, N-(2-methylphenyl)maleimide,N-(4-methylphenyl)maleimide, N-(2,6-dimethylphenyl)maleimide,N-(2,6-diethylphenyl)maleimide, N-(2-methoxyphenyl)maleimide,N-benzylmaleimide, N-dodecylmaleimide, N-isopropylmaleimide, andN-cyclohexylmaleimide.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the component (C) is at least onemaleimide compound represented by the following general formula (2):

wherein each R₂ is —C(Xc)₂—, —CO—, —O—, —S—, —SO₂—, or a single bond,and each R₂ may be the same or different, and each Xc is an alkyl grouphaving 1 to 4 carbon atoms, —CF₃, —OCH₃, —NH₂, a halogen atom, or ahydrogen atom, and each Xc may be the same or different, and theirsubstitution positions on the benzene are independent of one another,and each of n and p represents an integer of 0 to 10.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the component (C) is at least onemaleimide compound selected from the group consisting of2,2-bis[4-(4-maleimidophenoxy)phenyl]propane,bis(3-ethyl-5-methyl-4-maleimidophenyl)methane,polyphenylmethanemaleimide, and bis(4-maleimidophenyl)methane.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the component (C) is at least onevinyl compound containing divinylbiphenyl.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the inorganic filler as component(D) is an inorganic filler selected from alumina, titanium oxide, mica,silica, beryllia, barium titanate, potassium titanate, strontiumtitanate, calcium titanate, aluminum carbonate, magnesium hydroxide,aluminum hydroxide, aluminum silicate, calcium carbonate, calciumsilicate, magnesium silicate, silicon nitride, boron nitride, clay suchas calcined clay, talc, aluminum borate, aluminum borate, and siliconcarbide, or a mixture of two or more inorganic fillers comprising atleast one of those.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the inorganic filler as component(D) is silica or strontium titanate having a particle size of 0.01 to 30μm.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the inorganic filler as component(D) has been subjected to surface treatment with at least one couplingagent selected from silane coupling agents and titanate coupling agents.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the inorganic filler as component(D) has been subjected to surface treatment with a vinylgroup-containing silane coupling agent.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the inorganic filler as component(D) is preliminarily dispersed in (F) an organic solvent to form aslurry, and then the slurry and the saturated thermoplastic elastomer(E) are mixed together.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the organic solvent as component(F) is at least one organic solvent comprising a ketone solvent.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the saturated thermoplasticelastomer as component (E) is at least one saturated thermoplasticelastomer comprising a saturated thermoplastic elastomer obtained byhydrogenating an unsaturated double bond-containing group in thebutadiene moiety of a styrene-butadiene copolymer.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the saturated thermoplasticelastomer as component (E) is preliminarily dissolved in (G) a secondorganic solvent, and then the resultant solution and the inorganicfiller (D) are mixed together.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the second organic solvent ascomponent (G) is at least one organic solvent comprising an aromatichydrocarbon solvent or a ketone solvent.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the amount of the component (A)incorporated is in the range of from 2 to 200 parts by weight, relativeto 100 parts by weight of the total amount of the components (B) and(C),

the amount of the component (C) incorporated is in the range of from 2to 200 parts by weight, relative to 100 parts by weight of the component(B), the amount of the component (D) incorporated is in the range offrom 1 to 1,000 parts by weight, relative to 100 parts by weight of thetotal amount of the components (A), (B), (C), and (E), and the amount ofthe component (E) incorporated is in the range of from 1 to 100 parts byweight, relative to 100 parts by weight of the total amount of thecomponents (A), (B), and (C).

The present invention is directed to the process for producing athermosetting resin varnish, which further comprises the step of adding(H) a radical reaction initiator.

The present invention is directed to the process for producing athermosetting resin varnish, which further comprises the step of adding(I) a crosslinkable monomer or crosslinkable polymer containing at leastone ethylenically unsaturated double bond-containing group in themolecule thereof.

The present invention is directed to the process for producing athermosetting resin varnish, wherein the component (I) is at least onecrosslinkable monomer or crosslinkable polymer containing anethylenically unsaturated double bond-containing group selected from thegroup consisting of chemically unmodified butadiene polymers andmaleimide compounds.

The present invention is directed to the process for producing athermosetting resin varnish, which further comprises the step of adding(J) at least one flame retardant selected from bromine flame retardantsand phosphorus flame retardants.

The present invention is directed to a thermosetting resin varnishcomprising: a thermosetting resin composition of an uncured semi-IPNcomposite having compatibilized with one another (A) a polyphenyleneether, (B) a butadiene polymer which contains in the molecule thereof40% or more of a 1,2-butadiene unit having a 1,2-vinyl group in the sidechain thereof, and which is not chemically modified, and (C) acrosslinking agent; (D) an inorganic filler; and (E) a saturatedthermoplastic elastomer.

The present invention is directed to the thermosetting resin varnish,which has a viscosity of 10 to 300 mPa·s at 25° C.

The present invention is directed to a resin varnish for printed circuitboard, obtained by using the above-mentioned process for producing athermosetting resin varnish.

The present invention is directed to a prepreg obtained by impregnatinga substrate with the above-mentioned resin varnish for printed circuitboard or the above-mentioned thermosetting resin varnish, and thendrying the resultant substrate at 60 to 200° C.

The present invention is directed to a metal-clad laminate obtained bystacking one or more sheets of the above-mentioned prepreg for printedcircuit board on one another to prepare a stacked prepreg, disposing ametallic foil on one side or both sides of the stacked prepreg, andpressing them together while heating.

Effect of the Invention

By the process for producing a resin varnish of the present invention,there can be provided a resin varnish, a prepreg, and a metal-cladlaminate, which are advantageous not only in that, when used in aprinted circuit board, they exhibit excellent high frequency propertiesand excellent moisture absorption dependency of them, excellent heatresistance (particularly, excellent heat resistance after moistureabsorption), and low thermal expansion properties, but also in that theyhave metallic foil peeling strength satisfactorily improved. Therefore,the present invention is advantageously used in the application of amember or part for printed circuit board for use in various electric orelectronic devices, e.g., mobile communication devices using highfrequency signals having, for example, a frequency of 1 GHz or more anddevices for their base stations, network-associated electronic devices,such as a server and a router, and large-size computers.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic view showing a thermosetting resin compositionof an uncured semi-IPN composite.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the preferred embodiment of the present invention will bedescribed in detail.

The reason why the thermosetting resin varnish of the present invention,which contains a polyphenylene ether-modified butadiene polymer which isa novel semi-IPN composite, an inorganic filler, and a saturatedthermoplastic elastomer, and which is obtained by a process in which theinorganic filler and saturated thermoplastic elastomer are preliminarilymixed together and then the resultant mixture and the polyphenyleneether-modified butadiene polymer are mixed together, can achieve theabove task is not clear. The reason is presumed by the present inventorsas follows, but the reason does not exclude connection with otherfactors.

In the present invention, a polyphenylene ether which is a thermoplasticresin having excellent dielectric properties, and a chemicallyunmodified butadiene polymer known as one of the thermosetting resinsexhibiting the most excellent dielectric properties after being curedare used as essential components to remarkably improve the dielectricproperties. As mentioned above, the polyphenylene ether and chemicallyunmodified butadiene polymer are inherently incompatible with eachother, and it has been difficult to obtain a homogeneous resincomposition from these resins. However, by the process of the presentinvention using a preliminary reaction, a varnish containing a resincomposition having a novel construction in which the resins arethoroughly compatibilized can be obtained.

In the present invention, the term “preliminary reaction” means togenerate radicals at a reaction temperature of, for example, 60 to 170°C. while preventing the solvent from volatilizing to effect a reactionof component (B) with component (C), so that a predetermined amount ofcomponent (B) is crosslinked and a predetermined amount of component (C)is converted. The mixture obtained after the preliminary reaction is anuncured state, i.e., a state such that gelation does not occur. Themixture of components (A), (B), and (C) before and after the preliminaryreaction and the semi-IPN polymer can be easily distinguished from eachother from a change of the viscosity, turbidity, or characteristic peakmeasured by, e.g., liquid chromatography or spectrophotometry. Forexample, when using an analytical instrument for, e.g., liquidchromatography or spectrophotometry, disappearance of the characteristicpeak of component (C) or reduction of the peak ratio is observed afterthe preliminary reaction.

In the present invention, the term “curing reaction” means to form aB-stage (semi-cured) rein in the application step (in the production ofa prepreg or the volatilization step for solvent in the formation of afilm), or to generate radicals at the temperature of heat pressing inthe production of a copper-clad laminate or solvent volatilizationtemperature or higher to cure a resin, and is totally different from thepreliminary reaction in the present invention. In other words, in thepresent invention, components (A), (B), and (C) are essential, and anuncured resin having component (A) and components (B) and (C)compatibilized with each other cannot be obtained unless the process ofthe present invention comprising the step for mixing components (A),(B), and (C) to effect a reaction while stirring is used. Therefore,when a B-stage (semi-cured) resin is formed using a general varnishhaving the above components merely mixed together, the prepreg or filmeven in a semi-cured state obtained after solvent volatilization suffersmacro phase separation. Further, the cured product using such a resinhas suffered phase separation, and hence is even poorer in properties,such as copper foil peeling strength, thermal expansion properties, heatresistance, and moisture absorption properties, than the compatibilized,cured product obtained by the present invention.

In the present invention, in the presence of a polyphenylene ether ascomponent (A), a butadiene polymer as component (B), which contains inthe molecule thereof 40% or more of a 1,2-butadiene unit having a1,2-vinyl group in the side chain thereof and which is not chemicallymodified, and a crosslinking agent as component (C) are preliminaryreacted so that a conversion rate of component (C) (reaction rate)becomes in an appropriate range to form a polyphenylene ether-modifiedbutadiene prepolymer which is in an uncured state such that the polymeris not completely cured and one linear polymer component {correspondingto component (A); portions depicted by the solid lines in FIG. 1} andthe other crosslinkable components {corresponding to components (B) and(C); portions depicted by the dotted lines in FIG. 1} together form aso-called “semi-IPN”, obtaining a resin varnish containing a homogeneousresin composition (thermosetting resin composition of uncured semi-IPNcomposite; see FIG. 1). The homogeneous (compatibilized) state of thisresin composition is not a state in which component (A) and the othercomponents {partially crosslinked product of components (B) and (C)}form chemical bonds, and is presumed to be an apparently homogenized(compatibilized) state in which the molecular chains of component (A)and the other components are partially and physically entwined with eachother into oligomers to form a micro phase separation structure.

From the resin composition containing the polyphenylene ether-modifiedbutadiene prepolymer (thermosetting resin composition of uncuredsemi-IPN composite), an apparently homogenized resin film can beobtained. In the mixture of a conventionally known polyphenyleneether-modified butadiene prepolymer or polyphenylene ether andpolybutadiene, or the mixture of a prepolymer obtained bypreliminary-reacting a polybutadiene homopolymer with a bismaleimidecompound and a polyphenylene ether, a semi-IPN is not formed and theconstituents are not compatibilized with each other, causing phaseseparation. Therefore, differing from the composition in the presentinvention, the mixture of a conventionally known polyphenyleneether-modified butadiene prepolymer or polyphenylene ether andpolybutadiene, or the mixture of a prepolymer obtained bypreliminarily-reacting a polybutadiene homopolymer with a bismaleimidecompound and a polyphenylene ether suffers apparently heterogeneousmacro phase separation.

A prepreg produced using a resin varnish containing a polyphenyleneether-modified butadiene prepolymer obtained by the process of thepresent invention (solution containing a thermosetting resin compositionof uncured semi-IPN composite) has smooth appearance, and solves theproblem of tackiness because the molecules of the butadiene prepolymercrosslinked to some extent and tack-free polyphenylene ether arecompatibilized with one another. Further, with respect to the metal-cladlaminate produced using the prepreg, there is no problem of theappearance like the prepreg, and the resin composition in the prepreg iscured in such a state that the molecular chains are partially andphysically entwined with each other, and therefore, as compared to thecured product of the resin composition in a heterogeneous state, theresultant cured product has an increased pseudocrosslinking density andhence has an improved elastic modulus, thus lowering the thermalexpansion coefficient. The improvement of the elastic modulus and theformation of the homogeneous micro phase separation structure canremarkably improve the breaking strength or heat resistance(particularly after moisture absorption) of the resin. Further, theresin improved in breaking strength can exhibit such a high metallicfoil peeling strength that a low-profile foil can be used in themetal-clad laminate. Furthermore, it has been found that, by selectingas component (C) a specific crosslinking agent forming a cured producthaving a feature such that the resin strength or toughness is improvedor the molecular motion is restricted, the metallic foil peelingstrength and thermal expansion properties can be improved.

Further, it has been found that, by using the polyphenyleneether-modified butadiene prepolymer in the present invention and theinorganic filler as component (D) in combination, not only can thereduction of thermal expansion coefficient, further improvement of heatresistance, and desired control of relative permittivity be achieved,which are generally known as the effect of the addition of inorganicfiller, but also the change of the dielectric properties after moistureabsorption (moisture absorption dependency) can be reduced whilesuppressing the deterioration of the dielectric properties. In addition,it has been found that, by using the saturated thermoplastic elastomeras component (E), not only can the impact resistance be improved, butalso further excellent dielectric properties can be imparted to theresin composition. Generally, as an impact resistance improving agentfor a polyphenylene ether or a compatibilizing agent for improving thecompatibility with a thermosetting resin having an unsaturated doublebond-containing group, an unsaturated thermoplastic elastomer, such as astyrene-butadiene copolymer, or a crosslinkable polymer is used incombination with a polyphenylene ether, but such a resin composition islowered in Tg (glass transition temperature). On the other hand, thesaturated thermoplastic elastomer which is the essential component inthe present invention is inherently less compatible with a butadienepolymer, but the polyphenylene ether-modified butadiene prepolymer inthe present invention is remarkably improved in the compatibility withthe thermoplastic elastomer, as compared to a conventional butadienepolymer, and, even when using the polyphenylene ether-modified butadieneprepolymer and the saturated thermoplastic elastomer in combination, theresultant resin composition does not sacrifice the homogenization(compatibilization). The saturated thermoplastic elastomer per se hasremarkably excellent dielectric properties, as compared to theunsaturated thermoplastic elastomer or crosslinkable polymer. Therefore,when it makes the resin composition containing such a saturatedthermoplastic elastomer, a cured product from the resin composition canobtain further excellent high frequency properties. Further, thesaturated thermoplastic elastomer has no co-curing properties with thethermosetting component, and the saturated thermoplastic elastomer andother components form a micro phase separation structure in the curedproduct, preventing the lowering of Tg.

However, when the inorganic filler as component (D) and the saturatedthermoplastic elastomer as component (E) are separately mixed into thepolyphenylene ether-modified polybutadiene polymer or the polyphenyleneether-modified polybutadiene solution containing a solvent, aggregationof the inorganic filler or phase separation or deposition of thethermoplastic elastomer occurs, so that the inorganic filler orthermoplastic elastomer settles in the resin varnish, making itdifficult to form a homogeneous resin varnish. Therefore, the prepregproduced using such a varnish has irregular appearance. Further, themetal-clad laminate produced using this prepreg disadvantageously hasnot only inconsistent dielectric properties but also increased waterabsorption due to the aggregation of the inorganic filler.

Various studies of the process for mixing these components have beenmade. As a result, it has been found that, by preliminarily mixingtogether the inorganic filler as component (D) and the saturatedthermoplastic elastomer as component (E) to obtain a mixture, and thenmixing together the mixture and polyphenylene ether-modified butadiene,the dispersibility of the inorganic filler is improved, making itpossible to produce a homogeneous resin varnish free from, e.g., phaseseparation or deposition of the saturated thermoplastic elastomer ascomponent (E). The temperature at which the mixture and polyphenyleneether-modified butadiene are mixed together is preferably 60° C. orlower, more preferably 55° C. or lower, especially preferably 50° C. orlower. When the temperature is 60° C. or lower, neither aggregation ofthe inorganic filler nor phase separation or deposition of the saturatedelastomer occurs, enabling the advantageous production of a varnish. Theprepreg produced using this varnish has excellent appearance, andfurther the metal-clad laminate produced using the prepreg exhibits notonly excellent dielectric properties but also reduced water absorptionand excellent heat resistance after moisture absorption.

The present invention is directed to a process for producing a resinvarnish containing a thermosetting resin composition, which contains anuncured semi-IPN composite, an inorganic filler, and a saturatedthermoplastic elastomer, wherein the process comprises the steps of:preliminary reacting, (B) a butadiene polymer which contains in themolecule thereof 40% or more of a 1,2-butadiene unit having a 1,2-vinylgroup in the side chain thereof, and which is not chemically modifiedand (C) a crosslinking agent, in the presence of (A) a polyphenyleneether to obtain a polyphenylene ether-modified butadiene prepolymerwhich is an uncured semi-IPN composite; mixing together (D) an inorganicfiller and (E) a saturated thermoplastic elastomer to obtain a mixture;and mixing together the obtained mixture and the polyphenyleneether-modified butadiene prepolymer. Specifically, the process forproducing a resin varnish containing a thermosetting resin compositionof a novel semi-IPN composite of the present invention is a process forproducing a resin varnish containing a polyphenylene ether-modifiedbutadiene prepolymer obtained by preliminarily-reacting (B) a butadienepolymer which contains in the molecule thereof 40% or more of a1,2-butadiene unit having a 1,2-vinyl group in the side chain thereof,and which is not chemically modified and (C) a crosslinking agent, inthe presence of (A) a polyphenylene ether, (D) an inorganic filler, and(E) a saturated thermoplastic elastomer, wherein the process comprisespreliminarily mixing together inorganic filler (D) and saturatedthermoplastic elastomer (E), and then mixing together the resultantmixture and the polyphenylene ether-modified butadiene prepolymer. Thecomponents of the resin varnish of the present invention, a preferredprocess for preparing the polyphenylene ether-modified butadieneprepolymer, and a preferred process for preparing the resin compositionare described below.

In the present invention, as examples of components (A) used in thepreparation of the polyphenylene ether-modified butadiene prepolymer,there can be mentioned poly(2,6-dimethyl-1,4-phenylene)ether orpoly(2,3,6-trimethyl-1,4-phenylene)ether obtained by homopolymerizationof 2,6-dimethylphenol or 2,3,6-trimethylphenol, and a copolymer of2,6-dimethylphenol and 2,3,6-trimethylphenol. A polymer alloy of theabove polymer and, e.g., polystyrene or a styrene-butadiene copolymer,i.e., so-called modified polyphenylene ether can be used, but, in thiscase, the polymer more preferably contains apoly(2,6-dimethyl-1,4-phenylene)ether component, apoly(2,3,6-trimethyl-1,4-phenylene)ether component, or a copolymercomponent of 2,6-dimethylphenol and 2,3,6-trimethylphenol in an amountof 50% or more.

With respect to the molecular weight of component (A), there is noparticular limitation, but, from the viewpoint of achieving good balancebetween the dielectric properties or heat resistance obtained when usedin a printed circuit board and the flowability of the resin obtainedwhen used in a prepreg, the number average molecular weight of component(A) is preferably in the range of from 7,000 to 30,000. The numberaverage molecular weight in the present invention is measured by gelpermeation chromatography utilizing a calibration curve obtained withrespect to standard polystyrene.

In the present invention, with respect to component (B) used in thepreparation of the polyphenylene ether-modified butadiene prepolymer,there is no particular limitation as long as it is a butadiene polymerwhich contains in the molecule thereof 40% or more of a 1,2-butadieneunit having a 1,2-vinyl group in the side chain thereof, and which isnot chemically unmodified. Specifically, component (B) is not modifiedpolybutadiene, of which 1,2-vinyl group in the side chain in themolecule or the both ends or one end is chemically modified into, e.g.,epoxide, glycol, phenol, maleic acid, (meth)acrylic acid, or urethane,but an unmodified butadiene polymer. When the unmodified polybutadieneis used, excellent dielectric properties, excellent resistance tomoisture, and excellent heat resistance after moisture absorption can bemaintained. When the butadiene polymer contains in the molecule thereof40% or more of a 1,2-butadiene unit having a 1,2-vinyl group, a certainamount of crosslinking points can be secured and the resultant resincomposition exhibits excellent curing properties, so that the dielectricproperties (particularly, dielectric loss tangent), heat resistance(particularly, heat resistance after moisture absorption), and thermalexpansion coefficient can satisfy the requirements for the applicationof the resin varnish to a printed circuit board.

From the viewpoint of achieving excellent curing properties of the resincomposition, the content of the 1,2-butadiene unit having a 1,2-vinylgroup in the side chain thereof in the molecule of component (B) is morepreferably 50% or more, further preferably 65% or more. From theviewpoint of achieving good balance between the curing properties of theresin composition or the dielectric properties of a cured product of theresin composition and the flowability of the resin obtained when used ina prepreg, the number average molecular weight of component (B) ispreferably in the range of from 500 to 10,000, more preferably 700 to8,000, further preferably 1,000 to 5,000. The number average molecularweight is as defined for the number average molecular weight ofcomponent (A).

Specific examples of components (B) preferably used in the presentinvention include commercially available products, such as B-1000,B-2000, B-3000 (trade names, manufactured by NIPPON SODA CO., LTD.),B-1000, B-2000, B-3000 (trade names, manufactured by NIPPON OILCORPORATION), and Ricon 142, Ricon 150, Ricon 152, Ricon 153, Ricon 154(trade names, manufactured by Sartomer Company).

In the present invention, component (C) used in the preparation of thepolyphenylene ether-modified butadiene prepolymer is a compound havingin the molecule thereof a functional group reactive to component (B),for example, a crosslinkable monomer or crosslinkable polymer containingat least one ethylenically unsaturated double bond-containing group inthe molecule thereof. Specific examples of components (C) include vinylcompounds, maleimide compounds, diallyl phthalate, (meth)acryloylcompounds, and unsaturated polyesters. Of these, preferred component (C)is at least one maleimide compound or at least one vinyl compoundbecause the maleimide or vinyl compound has excellentco-crosslinkability with component (B) and hence the resultant resincomposition has excellent curing properties and excellent storagestability, and there can be obtained excellent total balance between theshapability of the resin composition used in a printed circuit board,dielectric properties, dielectric properties after moisture absorption,thermal expansion properties, metallic foil peeling strength, Tg, heatresistance after moisture absorption, and flame retardancy.

A maleimide compound preferably used as component (C) in the presentinvention can be a compound containing at least one maleimido group inthe molecule thereof and being represented by the general formula (1)below. A monomaleimide compound or polymaleimide compound can bepreferably used, and is represented by the general formula (1), (2),(3), (4), or (5) below.

wherein R₁ is a monovalent or multivalent organic group having a valenceof m, and being any one of aliphatic, alicyclic, aromatic andheterocyclic, Xa and Xb may be the same or different and each is amonovalent atom or organic group selected from a hydrogen atom, ahalogen atom, and an aliphatic organic group, and m represents aninteger of 1 or more.

Each of Xa and Xb is preferably a hydrogen atom, and R₁ is preferably aphenyl group, an alkylphenyl group, a dialkylphenyl group, or analkoxyphenyl group. As an example of formula (1), there can be mentionedthe following formula (5).

wherein:R₃ represents a monovalent or divalent aliphatic, alicyclic, aromatic,or heterocyclic organic group, ands represents 0 or 1,wherein when s is 0 and R₃ is a monovalent group, R₃ is preferably alinear or branched alkyl group having 1 to 18 carbon atoms, a cycloalkylgroup having 3 to 8 carbon atoms, an aralkyl group having 7 to 15 carbonatoms, or an unsubstituted aryl group having 6 to 18 carbon atoms or anaryl group having 6 to 18 carbon atoms substituted with an alkyl grouphaving 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbonatoms, andwherein when s is 1 and R₃ is a divalent group, R₃ is preferably analkylene group having 1 to 18 carbon atoms in total, an arylene grouphaving 6 to 15 carbon atoms in total, or acycloalkylene-alkylene-cycloalkylene group having 7 to 18 carbon atomsin total.

Formula (5) wherein s is 0 corresponds to formula (1) wherein m is 1 andeach of Xa and Xb is a hydrogen atom. Formula (5) wherein s is 1corresponds to formula (1) wherein m is 2 and each of Xa and Xb is ahydrogen atom.

wherein each R₂ is —C(Xc)₂—, —CO—, —O—, —S—, —SO₂—, or a single bond,and each R₂ may be the same or different, and each Xc is an alkyl grouphaving 1 to 4 carbon atoms, —CF₃, —OCH₃, —NH₂, a halogen atom, or ahydrogen atom, and each Xc may be the same or different, and theirsubstitution positions on the benzene are independent of one another,and each of n andp represents 0 or an integer of 1 to 10.

Specific examples of monomaleimide compounds represented by the generalformula (1) or (5) include N-phenylmaleimide,N-(2-methylphenyl)maleimide, N-(4-methylphenyl)maleimide,N-(2,6-dimethylphenyl)maleimide, N-(2,6-diethylphenyl)maleimide,N-(2-methoxyphenyl)maleimide, N-benzylmaleimide, N-dodecylmaleimide,N-isopropylmaleimide, and N-cyclohexylmaleimide.

Specific examples of polymaleimide compounds represented by the generalformula (2) or (5) include 1,2-dimaleimidoethane,1,3-dimaleimidopropane, bis(4-maleimidophenyl)methane,bis(3-ethyl-4-maleimidophenyl)methane,bis(3-ethyl-5-methyl-4-maleimidophenyl)methane, 2,7-dimaleimidofluorene,N,N′-(1,3-phenylene)bismaleimide,N,N′-[1,3-(4-methylphenylene)]bismaleimide, bis(4-maleimidophenyl)sulfone, bis(4-maleimidophenyl)sulfide, bis(4-maleimidophenyl)ether,1,3-bis(3-maleimidophenoxy)benzene,1,3-bis[3-(3-maleimidophenoxy)phenoxy]benzene,bis(4-maleimidophenyl)ketone,2,2-bis[4-(4-maleimidophenoxy)phenyl]propane,bis[4-(4-maleimidophenoxy)phenyl]sulfone,bis[4-(4-maleimidophenoxy)phenyl]sulfoxide,4,4′-bis(3-maleimidophenoxy)biphenyl,1,3-bis[2-(3-maleimidophenyl)propyl]benzene,1,3-bis{1-[4-(3-maleimidophenoxy)phenyl]-1-propyl} benzene,bis(maleimidocyclohexyl)methane,2,2-bis[4-(3-maleimidophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane,bis(maleimidophenyl)thiophene, and aliphatic, alicyclic, aromatic, orheterocyclic polymaleimides represented by the general formula (3) or(4) below (including their isomers). From the viewpoint of achievingexcellent resistance to moisture, excellent heat resistance, highbreaking strength, high metallic foil peeling strength, and low thermalexpansion properties when used in a printed circuit board, preferred arearomatic polymaleimides. Of these, especially from the viewpoint ofachieving further reduced thermal expansion coefficient,bis(3-ethyl-5-methyl-4-maleimidophenyl)methane is more preferably used,and, from the viewpoint of achieving further increased breaking strengthand metallic foil peeling strength,2,2-bis[4-(4-maleimidophenoxy)phenyl]propane is more preferably used.From the viewpoint of improving the shapability of the resin varnishused in a prepreg, preferred is monomaleimide which causes a slow curingreaction, and, of these, from the viewpoint of reducing the cost,N-phenylmaleimide is more preferably used. These maleimide compounds canbe used individually or in combination, and at least one of themaleimide compounds and at least one of the above-mentioned crosslinkingagents can be used in combination.

With respect to component (C), when the maleimide compound and acrosslinking agent are used in combination, the content of the maleimidecompound in component (C) is preferably 50% by weight or more, morepreferably 80% by weight or more, especially preferably 100% by weight,that is, component (C) is comprised only of the maleimide compound.

wherein q is 0 to 10 on an average.

wherein r is 0 to 10 on an average.

Examples of vinyl compounds preferably used as component (C) includestyrene, divinylbenzene, vinyltoluene, and divinylbiphenyl. Preferred isdivinylbiphenyl.

Specific examples of compounds preferably used as component (C) in thepresent invention include commercially available products, such asdivinylbiphenyl (manufactured by Nippon Steel Chemical Co. Ltd.).

In the present invention, the polyphenylene ether-modified butadieneprepolymer in the thermosetting resin composition of a novel semi-IPNcomposite is prepared by preliminarily-reacting component (B) andcomponent (C), in the presence of component (A) preferably developed ina medium, so that no gelation occurs. In this case, components (A), (B),and (C), which are inherently incompatible with one another, form asemi-IPN polymer in which the molecular chains are physically entwinedwith each other, obtaining an apparently homogenized (compatibilized)prepolymer in an uncured state such that the polymer is not completelycured.

In the present invention, the polyphenylene ether-modified butadieneprepolymer can be prepared by developing component (A) in a medium, forexample, dissolving component (A) in a solvent, and then dissolving ordispersing components (B) and (C) in the solution and heating theresultant solution or dispersion at 60 to 170° C. while stifling for 0.1to 20 hours. When the polyphenylene ether-modified butadiene prepolymeris prepared in the form of a solution, it is preferred that the amountof the solvent used is controlled so that the solids content(nonvolatile content) of the solution becomes generally 5 to 80% byweight. The solvent can be completely removed from the preparedpolyphenylene ether-modified butadiene prepolymer by, e.g.,concentration to form a resin composition free of solvent, or thepolyphenylene ether-modified butadiene prepolymer solution having theprepared prepolymer dissolved or dispersed in the solvent can be used.The solution having a solids content (nonvolatile content) increased by,e.g., concentration can be used.

With respect to the solvent, there is no particular limitation, butpreferred is at least one solvent comprising an aromatic hydrocarbonsolvent. Specific preferred examples of aromatic hydrocarbon solventsinclude toluene, xylene, and mesitylene, and these solvents can be usedindividually or in combination. In the solvent, the aromatic hydrocarbonsolvent and another solvent can be used in combination, and, withrespect to the solvent used in combination with the aromatic hydrocarbonsolvent, there is no particular limitation, but specific examplesinclude alcohols, such as methanol, ethanol, and butanol; ethers, suchas ethyl cellosolve, butyl cellosolve, ethylene glycol monomethyl ether,carbitol, and butyl carbitol; ketones, such as acetone, methyl ethylketone, methyl isobutyl ketone, and cyclohexanone; esters, such asmethoxyethyl acetate, ethoxyethyl acetate, butoxyethyl acetate, andethyl acetate; and nitrogen-containing solvents, such asN,N-dimethylformamide, N,N-dimethylacetamide, andN-methyl-2-pyrrolidone. These solvents can be used individually or incombination. When a mixed solvent of the aromatic hydrocarbon solventand another solvent is used, the content of the aromatic hydrocarbonsolvent in the mixed solvent is preferably 50% by weight or more, morepreferably 70% by weight or more, further preferably 80% by weight ormore.

In the resin composition in the present invention, with respect to theamount of each of components (A), (B), and (C) used in the preparationof the polyphenylene ether-modified butadiene prepolymer, the amount ofcomponent (A) incorporated is preferably in the range of from 2 to 200parts by weight, more preferably 10 to 100 parts by weight, furtherpreferably 15 to 50 parts by weight, relative to 100 parts by weight ofthe total of components (B) and (C). From the viewpoint of achievinggood balance between the thermal expansion coefficient, dielectricproperties, application workability ascribed to the viscosity of theresin varnish, and shapability of the varnish used in a printed circuitboard ascribed to the melt viscosity of the varnish in a prepreg, theamount of component (A) incorporated is preferably determined relativeto 100 parts by weight of the total of components (B) and (C). Theamount of component (C) incorporated is preferably in the range of from2 to 200 parts by weight, more preferably 5 to 100 parts by weight,further preferably 10 to 75 parts by weight, relative to 100 parts byweight of component (B). From the viewpoint of achieving good balancebetween the thermal expansion coefficient, Tg, metallic foil peelingstrength, and dielectric properties, the amount of component (C)incorporated is preferably determined relative to 100 parts by weight ofcomponent (B).

The polyphenylene ether-modified butadiene prepolymer in the presentinvention is generally obtained in the preparation thereof by apreliminary reaction so that the conversion rate of component (C)(reaction rate) is in the range of from 5 to 100%. A more preferredrange of the conversion rate of component (C) varies depending on theamounts of components (B) and (C) incorporated. When the amount ofcomponent (C) incorporated is in the range of from 2 to 10 parts byweight, relative to 100 parts by weight of component (B), the conversionrate of component (C) (reaction rate) is more preferably in the range offrom 10 to 100%; when the amount of component (C) is in the range offrom 10 to 75 parts by weight, the conversion rate of component (C)(reaction rate) is more preferably in the range of from 15 to 70%,especially preferably 25 to 40%; when the amount of component (C) is inthe range of from 75 to 100 parts by weight, the conversion rate ofcomponent (C) (reaction rate) is more preferably in the range of from 7to 90%; and when the amount of component (C) is in the range of from 100to 200 parts by weight, the conversion rate of component (C) (reactionrate) is more preferably in the range of from 5 to 80%. From theviewpoint of obtaining a resin composition or prepreg which appears tobe homogeneous and which is tack-free and achieving excellent heatresistance after moisture absorption, high metallic foil peelingstrength, and excellent thermal expansion coefficient when used in aprinted circuit board, the conversion rate of component (C) (reactionrate) is preferably 5% or more.

In the present invention, the polyphenylene ether-modified butadieneprepolymer involves one which is obtained by a reaction at a component(C) conversion rate of 100% and one which is obtained by a reaction at acomponent (C) conversion rate of less than 100% and which containscomponent (C) remaining unreacted or unconverted.

The conversion rate of component (C) (reaction rate) is determined fromthe amount of component (C) remaining in the polyphenyleneether-modified butadiene prepolymer, as measured by gel permeationchromatography, and the preliminarily formed calibration curve forcomponent (C).

In the process of the present invention, components (D) and (E) arepreliminarily mixed together, and the resultant mixture and thepolyphenylene ether-modified butadiene polymer obtained bypreliminarily-reacting components (A) to (C) are mixed together toobtain a thermosetting resin varnish. In the process of the presentinvention, components (D) and (E) are preliminarily mixed together, andtherefore component (E) serves as a compatibilizing agent for component(D) and the polyphenylene ether-modified butadiene polymer, improvingthe dispersibility of the inorganic filler as component (D). Thetemperature at which the mixture and the polyphenylene ether-modifiedbutadiene polymer are mixed together is further preferably 60° C. orlower because the dispersibility of component (D) is further improved.In contrast, when the inorganic filler as component (D) or the saturatedthermoplastic elastomer as component (E) is individually mixed with thepolyphenylene ether-modified butadiene polymer, aggregation of theinorganic filler or phase separation or deposition of the elastomeroccurs, and a printed circuit board using the resultant resin varnishhas low levels of the relative permittivity, dielectric loss tangent,transmission loss, and moisture absorption dependency of the dielectricproperties, as compared to that using the polyphenylene ether-modifiedbutadiene polymer in the process of the present invention comprising thestep for preliminarily mixing together the inorganic filler as component(D) and the saturated thermoplastic elastomer as component (E) to obtaina mixture. A mixture having components (D) and (E) mixed together may beeither a mixture of inorganic filler (D) and saturated thermoplasticelastomer (E) or a mixture of a slurry, which is obtained bypreliminarily dispersing component (D) in organic solvent (F), and asolution, which is obtained by preliminarily dissolving elastomer (E) insecond organic solvent (G).

With respect to the inorganic filler as component (D) in the presentinvention, there is no particular limitation, but specific examples ofusable inorganic fillers include alumina, titanium oxide, mica, silica,beryllia, barium titanate, potassium titanate, strontium titanate,calcium titanate, aluminum carbonate, magnesium hydroxide, aluminumhydroxide, aluminum silicate, calcium carbonate, calcium silicate,magnesium silicate, silicon nitride, boron nitride, clay such ascalcined clay, talc, aluminum borate, and silicon carbide. Theseinorganic fillers can be used individually or in combination. Withrespect to the form and particle size of the inorganic filler, there isno particular limitation, but an inorganic filler preferably having aparticle size of 0.01 to 30 μm, more preferably 0.1 to 15 μm isadvantageously used. When an inorganic filler having a particle size of0.01 μm or less is used, the flowability of the thermosetting resin islowered and therefore the shapability of the resin is poor when forminga prepreg or a metal-clad laminate, so that voids and others are likelyto be caused, and further the inorganic filler having such a smallparticle size has a large surface area and hence has reduced bond areabetween the metal and the resin, disadvantageously lowering the peelingstrength in a printed circuit board. On the other hand, when aninorganic filler having a particle size of more than 30 μm is used, theinsulation reliability of the wirings and insulating layer in a printedcircuit board disadvantageously is lowered.

In the present invention, it is desired that inorganic filler ascomponent (D) has been subjected to surface treatment with at least onecoupling agent selected from silane coupling agents and titanatecoupling agents. When the inorganic filler treated with the couplingagent is used, the adhesion of the surface of the inorganic filler tothe resin is improved, thus lowering the water absorption and improvingthe heat resistance after moisture absorption and the adhesion to themetal. As a silane coupling agent, carbon functional silane is used, andexamples include epoxy group-containing silanes, such as3-glycidoxypropyltrimethoxysilane,3-glycidoxypropyl(methyl)dimethoxysilane, and2-(2,3-epoxycyclohexyl)ethyltrimethoxysilane; amino group-containingsilanes, such as 3-aminopropyltriethoxysilane,N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, andN-(2-aminoethyl)-3-aminopropyl(methyl)dimethoxysilane; cationic silanes,such as 3-(trimethoxysilyl)propyltetramethylammonium chloride; vinylgroup-containing silanes, such as vinyltriethoxysilane; acrylgroup-containing silanes, such as 3-methacryloxypropyltrimethoxysilane;and mercapto group-containing silanes, such as3-mercaptopropyltrimethoxysilane. Of these, a vinyl group-containingsilane is especially preferably used because it is capable of reactingwith the polyphenylene ether-modified butadiene polymer and is lesspolar and therefore, the water absorption can be further reduced and theheat resistance after moisture absorption and the adhesion to the metalcan be improved. On the other hand, examples of titanate coupling agentsinclude alkyl titanates, such as titanium propoxide and titaniumbutoxide. These coupling agents or silicone polymers can be usedindividually or in combination.

With respect to the amount of the coupling agent attached to theinorganic filler as component (D) in the present invention, there is noparticular limitation, but, from the viewpoint of achieving excellentdispersibility of the inorganic filler in the resin material orobtaining a cured product having excellent heat resistance, the amountof the coupling agent attached is generally preferably 0.01 to 20% byweight, preferably 0.05 to 10% by weight, more preferably 0.1 to 7% byweight, based on the weight of the inorganic filler.

When a coupling agent is used, with respect to the process of treatingcomponent (D) with the coupling agent, there is no particularlimitation, but there can be employed either a process in whichcomponent (D) is preliminarily subjected to surface treatment by a wetprocess or a dry process, or a process in which, after the inorganicfiller and saturated thermoplastic resin elastomer are mixed together orafter the polyphenylene ether-modified butadiene prepolymer or the likeis added thereto, a coupling agent is mixed with the resultant mixturefor surface treatment of the inorganic filler. It is desired thatcomponent (D) preliminarily surface-treated is used. In this case, whenthe surface treatment is conducted by a wet process, the surface-treatedinorganic filler can be used in the form of a slurry having the couplingagent and inorganic filler dispersed in, e.g., the organic solvent ascomponent (F)(dispersing medium). When the surface treatment isconducted by a dry process, the surface-treated inorganic filler can beused in the form of a slurry having the treated inorganic fillerdispersed in, e.g., organic solvent (F). With respect to the conditionsfor the surface treatment including time and temperature, there is noparticular limitation.

In the present invention, it is preferred that the inorganic filler ascomponent (D) is preliminarily dispersed in organic solvent (F) to forma slurry and then the slurry and saturated thermoplastic elastomer (E)are mixed together. When the slurry is preliminarily formed, not only bethe dispersibility of the inorganic filler improved, but also thedispersibility of the inorganic filler is also excellent after mixedinto the resin, making it possible to further improve the heatresistance after moisture absorption and reduce the water absorption.

In the present invention, it is preferred that the organic solvent ascomponent (F) is at least one organic solvent comprising a ketonesolvent. In this case, the dispersibility of the inorganic filler isfurther improved. As a ketone solvent, for example, acetone, methylethyl ketone, methyl isobutyl ketone, or cyclohexanone is used. Thesesolvents can be used individually or in combination.

In the resin composition in the present invention, the amount ofcomponent (D) incorporated is preferably 1 to 1,000 parts by weight,more preferably 5 to 500 parts by weight, further preferably 10 to 350parts by weight, relative to 100 parts by weight of the total ofcomponents (A), (B), (C), and (E), and the amount of component (D) canbe appropriately selected depending on the desired control of therelative permittivity, desired improvement of the heat resistance, anddesired shapability of the prepreg. Further, with respect to the amountof component (D) and the amount of component (E) in the resincomposition in the present invention, from the viewpoint of obtaining ahomogeneous resin varnish free from aggregation of the inorganic filleror phase separation or deposition of the thermoplastic elastomer, theamount of component (E) incorporated is preferably 5 to 500 parts byweight, more preferably 10 to 300 parts by weight, relative to 100 partsby weight of component (D).

With respect to component (E) in the present invention, there is noparticular limitation as long as it is a saturated thermoplasticelastomer, but a styrene saturated thermoplastic elastomer havingexcellent compatibility with component (A) is desired. Specific examplesof components (E) preferably used in the present invention includestyrene-ethylene-butylene copolymers, which can be obtained by, e.g., aprocess comprising hydrogenating an unsaturated double bond-containingportion in the butadiene block of a styrene-butadiene copolymer. Whenthe styrene saturated thermoplastic elastomer is used, from theviewpoint of achieving good balance between the compatibility of theelastomer with the polyphenylene ether-modified butadiene prepolymer andthe thermal expansion properties obtained after the resin composition iscured, the styrene saturated thermoplastic elastomer preferably has astyrene block content of 20 to 70%. As component (E), a chemicallymodified saturated thermoplastic elastomer having in the moleculethereof a functional group, such as an epoxy group, a hydroxyl group, acarboxyl group, an amino group, or an acid anhydride, can be used. Withrespect to component (E), the saturated thermoplastic elastomers can beused individually or in combination, and, when using the styrenesaturated thermoplastic elastomer, two types or more of the elastomershaving different styrene contents can be used in combination.

In the present invention, it is preferred that the saturatedthermoplastic elastomer as component (E) is preliminarily dissolved in(G) a second organic solvent and then the resultant solution andinorganic filler (D) are mixed together. In this case, the saturatedthermoplastic elastomer, which per se has low solubility and isdifficult to dissolve in the presence of another resin material, can beeasily dissolved.

In the present invention, it is preferred that the second organicsolvent as component (G) is at least one organic solvent comprising anaromatic hydrocarbon solvent or a ketone solvent. In this case, thesolubility of the saturated thermoplastic elastomer becomes furtherexcellent. As an aromatic hydrocarbon solvent, for example, toluene,xylene, or mesitylene is preferred. As a ketone solvent, for example,acetone, methyl ethyl ketone, methyl isobutyl ketone, or cyclohexanoneis preferred. These solvents can be used individually or in combination.

In the resin composition in the present invention, the amount ofcomponent (E) incorporated is preferably 1 to 100 parts by weight, morepreferably 2 to 50 parts by weight, further preferably 5 to 30 parts byweight, relative to 100 parts by weight of the total of components (A),(B), and (C). When the amount of component (E) incorporated is less than1 part by weight, the effect of improving the dielectric propertiestends to be unsatisfactory. On the other hand, when the amount ofcomponent (E) is more than 100 parts by weight, the thermal expansionproperties of the cured product tend to become poor.

In the present invention, for the purpose of initiating or promoting thepreliminary reaction of components (B) and (C) in the preparation of thepolyphenylene ether-modified butadiene prepolymer and for the purpose ofinitiating or promoting the curing reaction of the resin compositioncontained in the prepreg in the production of the metal-clad laminate ormultilayer printed circuit board, it is preferred that the resin varnishcontains (H) a radical reaction initiator.

Specific examples of components (H) include peroxides, such as dicumylperoxide, t-butylcumyl peroxide, benzoyl peroxide, cumene hydroperoxide,1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(t-butylperoxy)-2-methylcyclohexane,1,1-bis(t-hexylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)cyclohexane,2,2-bis[4,4-di(t-butylperoxy)cyclohexyl]propane,2,5-dimethylhexane-2,5-dihydroperoxide,2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3, di-t-butylperoxide,α,α′-bis(t-butylperoxy)diisopropylbenzene,2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, di-t-butylperoxyisophthalate, t-butyl peroxybenzoate, t-butyl peroxyacetate,2,2-bis(t-butylperoxy)butane, 2,2-bis(t-butylperoxy)octane,2,5-dimethyl-2,5-di(benzoylperoxy)hexane,bis(t-butylperoxy)isophthalate, isobutyryl peroxide,di(trimethylsilyl)peroxide, and trimethylsilyl triphenylsilyl peroxide;2-hydroxy-2-methyl-1-phenylpropan-1-one,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, benzoin methylether, and methyl-o-benzoyl benzoate, but the radical reaction initiatoris not limited to these compounds.

With respect to component (H), it is preferred that the initiator usedfor initiating or promoting the preliminary reaction in the preparationof the polyphenylene ether-modified butadiene prepolymer and theinitiator used for initiating or promoting the curing reaction after thepreparation of the polyphenylene ether-modified butadiene prepolymer areseparately added before and after the preparation of the polyphenyleneether-modified butadiene prepolymer. In this case, these initiators usedas component (H) may be the same or different, and the initiators foreach purpose can be used individually or in combination.

With respect to the initiator used for initiating or promoting thepreliminary reaction, preferred are peroxyketal organic peroxides, suchas 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(t-butylperoxy)-2-methylcyclohexane,1,1-bis(t-hexylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)cyclohexane,and 2,2-bis[4,4-di(t-butylperoxy)cyclohexyl]propane, and, of these, morepreferred are 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(t-hexylperoxy)cyclohexane, and1,1-bis(t-butylperoxy)cyclohexane, and these compounds can be usedindividually or in combination. With respect to the initiator used forinitiating or promoting the curing reaction after the preparation of thepolyphenylene ether-modified butadiene prepolymer, preferred are dialkylperoxide organic peroxides, such as dicumyl peroxide, t-butylcumylperoxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3, di-t-butylperoxide, α,α′-bis(t-butylperoxy)diisopropylbenzene, and2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, and, of these, dicumylperoxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3, andα,α′-bis(t-butylperoxy)diisopropylbenzene are preferred, and thesecompounds can be used individually or in combination.

In the present invention, the amount of component (H) incorporated canbe determined according to the amounts of components (B) and (C)incorporated, and is preferably 0.05 to 10 parts by weight, relative to100 parts by weight of the total of components (B) and (C). When theamounts of the radical reaction initiators as component (H) separatelyadded before and after the preparation of the polyphenyleneether-modified butadiene prepolymer are in the above range, anappropriate reaction rate can be obtained in the preliminary reaction inthe preparation of the polyphenylene ether-modified butadiene prepolymerand excellent curing properties can be obtained in the curing reactionin the production of the metal-clad laminate or multilayer printedcircuit board.

In the process of the present invention, (I) a crosslinkable monomer orcrosslinkable polymer containing at least one ethylenically unsaturateddouble bond-containing group in the molecule thereof, (J) at least oneflame retardant selected from bromine flame retardants and phosphorusflame retardants, a thermosetting resin, a thermoplastic resin, and/oran additive can be optionally further added in such an amount thatproperties required when used in a printed circuit board, such asdielectric properties, heat resistance, adhesion (e.g., metallic foilpeeling strength, and adhesion to a substrate of glass or the like),resistance to moisture, Tg, and thermal expansion properties, are notsacrificed.

With respect to (I) crosslinkable monomer or crosslinkable polymercontaining at least one ethylenically unsaturated double bond-containinggroup in the molecule thereof, there is no particular limitation, and itis separate from the compound added in the preparation of thepolyphenylene ether-modified butadiene prepolymer. Specifically,component (I) is selected from the group consisting of chemicallyunmodified butadiene polymers and maleimide compounds, and the compoundsmentioned above as examples of components (B) and (C) can be used. Asexamples of chemically unmodified butadiene polymers, there can bementioned chemically unmodified butadiene polymers having a numberaverage molecular weight of more than 10,000. These compounds can beused individually or in combination. When the compound mentioned aboveas examples of components (B) and (C) is used as component (I), thecompound used as component (I) is separate from the compound added inthe preparation of the polyphenylene ether-modified butadieneprepolymer, and therefore, in this case, the amount of component (I)incorporated is distinguished from the amounts of components (B) and (C)incorporated, and a preferred amount of component (I) is separatelyshown below. When the compound mentioned above as examples of components(B) and (C) is used as component (I), it may be the same as or differentfrom the compound used in the preparation of the polyphenyleneether-modified butadiene prepolymer.

When a chemically unmodified butadiene polymer having a number averagemolecular weight of more than 10,000 is used as component (I), eitherone in a liquid state or one in a solid state can be used, and, withrespect to the 1,2-vinyl bond ratio and 1,4-bond ratio in the butadienepolymer, there is no particular limitation.

In the present invention, with respect to the amount of component (I)incorporated, there is no particular limitation, but the amount ofcomponent (I) incorporated is preferably 2 to 100 parts by weight, morepreferably 2 to 80 parts by weight, further preferably 2 to 60 parts byweight, relative to 100 parts by weight of the total of components (A),(B), and (C). When the amount of component (I) incorporated is 100 partsby weight or less, the lowering of the compatibility with thepolyphenylene ether-modified butadiene prepolymer or the lowering of Tgis advantageously unlikely to occur.

With respect to the flame retardant as component (J), there is noparticular limitation, but, for example, a bromine, phosphorus, or metalhydroxide flame retardant is preferably used. More specifically,examples of the bromine flame retardants include brominated epoxyresins, such as brominated bisphenol A epoxy resins and brominatedphenolic novolac epoxy resins; brominated addition-type flameretardants, such as hexabromobenzene, pentabromotoluene,ethylenebis(pentabromophenyl), ethylenebistetrabromophthalimide,1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane, tetrabromocyclooctane,hexabromocyclododecane, bis(tribromophenoxy)ethane, brominatedpolyphenylene ether, brominated polystyrene, and2,4,6-tris(tribromophenoxy)-1,3,5-triazine; and brominated reactiveflame retanrdants containing a group having an unsaturated double bond,such as tribromophenylmaleimide, tribromophenyl acrylate, tribromophenylmethacrylate, tetrabromobisphenol A dimethacrylate, pentabromobenzylacrylate and styrene bromide.

Examples of the phosphorus flame retardants include aromatic phosphoricacid esters, such as triphenyl phosphate, tricresyl phosphate,trixylenyl phosphate, cresyl diphenyl phosphate, cresyl di-2,6-xylenylphosphate, and resorcinol bis(diphenyl phosphate); phosphonic acidesters, such as divinyl phenylphosphonate, diallyl phenylphosphonate,and bis(1-butenyl) phenylphosphonate; phosphinic acid esters, such asphenyl diphenylphosphinate, methyl diphenylphosphinate, and9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide derivatives;phosphazene compounds, such as bis(2-allylphenoxy)phosphazene anddicresylphosphazene; melamine phosphate, melamine pyrophosphate,melamine polyphosphate, melam polyphosphate, ammonium polyphosphate,phosphorus-containing vinylbenzyl compounds, and red phosphorus.Examples of the metal hydroxide flame retardants include magnesiumhydroxide and aluminum hydroxide. These flame retardants can be usedindividually or in combination.

In the present invention, with respect to the amount of component (J)incorporated, there is no particular limitation, but the amount ofcomponent (J) incorporated is preferably 5 to 200 parts by weight, morepreferably 5 to 150 parts by weight, further preferably 5 to 100 partsby weight, relative to 100 parts by weight of the total of components(A), (B), and (C). When the amount of the flame retardant incorporatedis less than 5 parts by weight, the resultant composition tends to haveunsatisfactory flame resistance. On the other hand, when the amount ofthe flame retardant is more than 200 parts by weight, the heatresistance or metallic foil peeling strength of the varnish used in aprinted circuit board tends to become poor.

With respect to the thermosetting resin optionally added in the presentinvention, there is no particular limitation, but specific examplesinclude epoxy resins, cyanate ester resins, phenolic resins, urethaneresins, melamine resins, benzoxazine resins, benzocyclobutene resins,and dicyclopentadiene resins, and, a curing agent or curing promoter forthe above thermosetting resin can also be used. With respect to thethermoplastic resin optionally added, there is no particular limitation,but specific examples include polyolefins and derivatives thereof, suchas polyethylene, polypropylene, polybutene, an ethylene-propylenecopolymer, and poly(4-methyl-pentene), polyesters and derivativesthereof, polycarbonate, polyacetal, polysulfone, (meth)acrylic acidester copolymers, polystyrene, acrylonitrile-styrene copolymers,acrylonitrile-styrene-butadiene copolymers, polyvinyl acetal, polyvinylbutyrals, polyvinyl alcohols, complete hydrogenation products ofpolybutadiene, polyether sulfone, polyether ketone, polyether imide,polyphenylene sulfite, polyamideimide, polyamide, thermoplasticpolyimide, and liquid crystalline polymers, such as aromatic polyesters.With respect to the additive, there is no particular limitation, butspecific examples include silane coupling agents, titanate couplingagents, antioxidants, thermal stabilizers, antistatic agents,ultraviolet light absorbers, pigments, colorants, and lubricants. Thesethermosetting resins, thermoplastic resins, and additives can be usedindividually or in combination.

In the present invention, the above-mentioned inorganic filler (D) orcomponent (D) dispersed in component (F) and saturated thermoplasticelastomer (E) or component (E) dissolved in component (G) arepreliminarily mixed together, and then the resultant mixture, thepolyphenylene ether-modified butadiene prepolymer obtained usingcomponents (A), (B), and (C), radical reaction initiator (H), andoptionally added crosslinkable monomer or crosslinkable polymer (I)containing at least one ethylenically unsaturated double bond-containinggroup in the molecule thereof, flame retardant (J), and thermosettingresin, thermoplastic resin, and additive are mixed with each other by aknown process and stirred to obtain a resin varnish.

The resin varnish of the present invention can be obtained by dissolvingor dispersing the above-described resin composition in the presentinvention in a solvent. When the polyphenylene ether-modified butadieneprepolymer is prepared in the form of a solution, there can be used thepolyphenylene ether-modified butadiene prepolymer free of solvent, whichis obtained by completely removing the solvent from the polyphenyleneether-modified butadiene prepolymer solution by, e.g., concentration, orthe polyphenylene ether-modified butadiene prepolymer solution can bedirectly used.

When the polyphenylene ether-modified butadiene prepolymer solution isused, for enabling addition of an optimum solvent to improve thesolubility or dispersibility of each of components (D) to (J){especiallyfor widening the range of the amount of the organic solvent used forpreliminarily dispersing or dissolving therein component (D) or (E)} orfor facilitating production of a resin varnish having an optimum solidscontent (nonvolatile content) or varnish viscosity in the preparation ofa prepreg (application) (for example, so that excellent appearance andan appropriate resin applied amount can be achieved), it is desired thatthe polyphenylene ether-modified butadiene prepolymer solution having asolids content (nonvolatile content) increased by, e.g., concentrationis used. The solution obtained after the concentration advantageouslyhas a nonvolatile content of 40% by weight or more, preferably 50% byweight, but the nonvolatile content of the solution can be appropriatelycontrolled according to the solubility or dispersibility in theabove-mentioned mixing of the components and the preparation of theoptimum resin varnish for the application workability for a prepreg.When mixing together components (D) and (E), the polyphenyleneether-modified butadiene prepolymer, and other components and stirringthem to prepare a varnish, an additional solvent can be added, and thesolvent listed above as examples of components (F) and (G) or a solventother than these solvents can be used in the preparation of the resinvarnish. With respect to the solvent other than components (F) and (G),there is no particular limitation, and an alcohol, an ether, an ester,or a nitrogen-containing solvent, such as N,N-dimethylformamide,N,N-dimethylacetamide, or N-methyl-2-pyrrolidone, is used, and specificexamples of the individual solvents include those listed above.

When forming a varnish, it is preferred that the amount of the solventused is controlled so that the solids content (nonvolatile content) ofthe resin varnish becomes 5 to 80% by weight, but the varnish can beprepared so as to have the optimum solids content (nonvolatile content)or varnish viscosity for the above-mentioned application workability fora prepreg. For example, the varnish preferably has a viscosity at 25°C., as measured using an E-type viscometer, of 10 to 300 mPa·s, morepreferably 20 to 200 mPa·s, especially preferably 30 to 150 mPa·s.

Using the above-described resin varnish obtained by the process of thepresent invention, the prepreg or metal-clad laminate of the presentinvention can be produced by a known process. For example, the prepregis obtained by impregnating a reinforced fiber substrate, such as aglass fiber or an organic fiber, with the resin varnish obtained by thepresent invention and then drying the resultant substrate in a dryingoven or the like at a temperature of generally 60 to 200° C., preferably80 to 170° C. for 2 to 30 minutes, preferably 3 to 15 minutes. Then, onesheet or a plurality of sheets of the prepreg are stacked on oneanother, and a metallic foil is disposed on one side or both sides ofthe stacked prepreg and they are heated and/or pressed together underpredetermined conditions to obtain a double-sided or single-sidedmetal-clad laminate. In this case, the heating can be performedpreferably at a temperature in the range of from 100 to 250° C., and thepressing can be performed preferably under a pressure in the range offrom 0.5 to 10.0 MPa. It is preferred that the heating and pressing areperformed simultaneously using, e.g., a vacuum press, and, in this case,these treatments are preferably performed for 30 minutes to 10 hours.The prepreg or metal-clad laminate produced as described above issubjected to circuit fabrication processing and bonding processing forforming a multilayer circuit, such as perforation, metal plating, andetching for metallic foil, in accordance with a known process to obtaina single-sided, double-sided, or multilayer printed circuit board.

The present invention is not limited to the above-described embodiments,and can be arbitrarily changed or modified as long as the object aimedat by the present invention is attained.

EXAMPLES

Hereinbelow, the present invention will be described in more detail withreference to the following Examples, which should not be construed aslimiting the scope of the present invention.

Preparation of Resin Varnish Preparation Example 1

(a) In a one-liter separable flask equipped with a thermometer, a refluxcondenser, a vacuum evaporator, and a stirrer were placed 350 parts byweight of toluene and 50 parts by weight of polyphenylene ether (S202A,manufactured by Asahi Kasei Chemicals Corporation; Mn: 16,000) ascomponent (A), and the solid component was dissolved by stirring at atemperature of 90° C. inside the flask. Then, to the resultant solutionwere added 100 parts by weight of a chemically unmodified butadienepolymer (B-3000, manufactured by NIPPON SODA CO., LTD.; Mn: 3,000;1,2-vinyl structure: 90%) as component (B), 40 parts by weight ofbis(4-maleimidophenyl)methane (BMI-1000, manufactured by DAIWA KASEICO., LTD.) as component (C), and methyl isobutyl ketone (MIBK) as asolvent in such an amount that the solids content (nonvolatile content)of the resultant solution became 30% by weight, and stirring wascontinued and dissolution or uniform dispersion of the components wasconfirmed. Then, the temperature of the resultant solution or dispersionwas increased to 110° C. While maintaining the temperature at 110° C.,0.5 part by weight of 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane(PERHEXA TMH, manufactured by NOF CORPORATION) as a reaction initiatorwas added to the solution or dispersion. A preliminary reaction was theneffected for about one hour while stirring to obtain a polyphenyleneether-modified butadiene prepolymer solution having (A) a polyphenyleneether, (B) chemically unmodified butadiene polymer, and (C) crosslinkingagent compatibilized with one another. A conversion rate of thebis(4-maleimidophenyl)methane in the polyphenylene ether-modifiedbutadiene prepolymer solution was measured by gel permeationchromatography. As a result, it was found that the conversion rate was33%. The conversion rate is a value obtained by subtracting the amountof unconverted bis(4-maleimidophenyl)methane (measured value) from 100.Then, the temperature of the solution in the flask was adjusted to 80°C. The solution was then concentrated while stirring so that the solidscontent of the solution became 45% by weight.

(b) Subsequently, 171 parts by weight (120 parts by weight in terms ofthe solids) of a slurry (solids content: 70% by weight; solvent: MIBK)of spherical silica (SO-25R, manufactured by Admatechs Co., Ltd.;average particle size: 0.5 μm) as component (D), which had preliminarilybeen subjected to surface treatment with vinyltrimethoxysilane(KBM-1003, manufactured by Shin-Etsu Chemical Co., Ltd.) in a treatedamount of 2% by weight using MIBK as component (F), and 120 parts byweight (30 parts by weight in terms of the solids) of a solution of asaturated thermoplastic elastomer {hydrogenation product of astyrene-butadiene copolymer; Tuftec H1043, styrene content: 67%,styrene-(ethylene-butylene)-styrene block polymer (SEBS), manufacturedby Asahi Kasei Chemicals Corporation} as component (E) preliminarilydissolved in toluene as component (G) were mixed together, and theabove-obtained polyphenylene ether-modified butadiene polymer solutionwas added to the resultant mixture. Then, 5 parts by weight ofα,α′-bis(t-butylperoxy)diisopropylbenzene (PERBUTYL P, manufactured byNOF CORPORATION) as component (H) was added to the mixture, followed byaddition of methyl ethyl ketone (MEK), to prepare a resin varnish(solids content: about 40% by weight) in Preparation Example 1.

Preparation Example 2

(a) A polyphenylene ether-modified butadiene prepolymer was obtained insubstantially the same manner as in Preparation Example 1 except that,instead of the bis(4-maleimidophenyl)methane used in item (a) ofPreparation Example 1, 30 parts by weight of polyphenylmethanemaleimide(BMI-2000, manufactured by DAIWA KASEI CO., LTD.) was used. A conversionrate of BMI-2000 in the polyphenylene ether-modified butadieneprepolymer solution was measured by gel permeation chromatography. As aresult, it was found that the conversion rate was 35%.

(b) Subsequently, into 50 parts by weight of MIBK as component (F) weremixed 110 parts by weight of spherical silica (SO-25R, manufactured byAdmatechs Co., Ltd.; average particle size: 0.5 μm) as component (D),2.4 parts by weight of p-styryltrimethoxysilane (KBM-1403, manufacturedby Shin-Etsu Chemical Co., Ltd.), and 120 parts by weight (30 parts byweight in terms of the solids) of a solution of a saturatedthermoplastic elastomer {hydrogenation product of a styrene-butadienecopolymer; Tuftec H1043, styrene content: 67%,styrene-(ethylene-butylene)-styrene block polymer (SEBS), manufacturedby Asahi Kasei Chemicals Corporation} as component (E) preliminarilydissolved in toluene as component (G) to form a mixed solution. To themixed solution was added the above-obtained polyphenylene ether-modifiedbutadiene polymer solution. Then, 5 parts by weight ofα,α′-bis(t-butylperoxy)diisopropylbenzene (PERBUTYL P, manufactured byNOF CORPORATION) as component (H) was added to the mixture, followed byaddition of methyl ethyl ketone (MEK), to prepare a resin varnish(solids content: about 40% by weight) in Preparation Example 2.

Preparation Example 3

(a) A polyphenylene ether-modified butadiene prepolymer was obtained insubstantially the same manner as in Preparation Example 1 except that,instead of the bis(4-maleimidophenyl)methane used in item (a) ofPreparation Example 1, 35 parts by weight of2,2-bis[4-(4-maleimidophenoxy)phenyl]propane (BMI-4000, manufactured byDAIWA KASEI CO., LTD.) was used. A conversion rate of BMI-4000 in thepolyphenylene ether-modified butadiene prepolymer solution was measuredby gel permeation chromatography. As a result, it was found that theconversion rate was 25%.

(b) Subsequently, a resin varnish (solids content: about 40% by weight)in Preparation Example 3 was prepared in substantially the same manneras in Preparation Example 1 except that, instead of KBM-1003 used as asurface treatment agent as component (D) in item (b) of PreparationExample 1, N-phenyl-3-aminopropyltrimethoxysilane (KBM-573, manufacturedby Shin-Etsu Chemical Co., Ltd.) was used, and that, instead of H1043 ascomponent (E), Tuftec H1051 {styrene content: 42%;styrene-(ethylene-butylene)-styrene block polymer (SEBS), manufacturedby Asahi Kasei Chemicals Corporation} was used.

Preparation Example 4

A polyphenylene ether-modified butadiene prepolymer was obtained insubstantially the same manner as in Preparation Example 1 except that,instead of the bis(4-maleimidophenyl)methane used in item (a) ofPreparation Example 1, 40 parts by weight ofbis(3-ethyl-5-methyl-4-maleimidophenyl)methane (BMI-5100, manufacturedby DAIWA KASEI CO., LTD.) was used. A conversion rate of BMI-5100 in thepolyphenylene ether-modified butadiene prepolymer solution was measuredby gel permeation chromatography. As a result, it was found that theconversion rate was 30%.

(b) Subsequently, a resin varnish (solids content: about 40% by weight)in Preparation Example 4 was prepared in substantially the same manneras in Preparation Example 1 except that, instead of H1043 used ascomponent (E) in item (b) of Preparation Example 1, Tuftec H1051 wasused.

Preparation Example 5

(a) A polyphenylene ether-modified butadiene prepolymer was obtained insubstantially the same manner as in Preparation Example 1 except that,instead of the bis(4-maleimidophenyl)methane used in item (a) ofPreparation Example 1, 15 parts by weight of N-phenylmaleimide(IMILEX-P, manufactured by NIPPON SHOKUBAI CO., LTD.) was used. Aconversion rate of IMILEX-P in the polyphenylene ether-modifiedbutadiene prepolymer solution was measured by gel permeationchromatography. As a result, it was found that the conversion rate was32%.

(b) Subsequently, 171 parts by weight (120 parts by weight in terms ofthe solids) of a slurry (solids content: 70% by weight; solvent: MIBK)of SO-25R as component (D), which had preliminarily been subjected tosurface treatment with vinyltrimethoxysilane (KBM-1003, manufactured byShin-Etsu Chemical Co., Ltd.) in a treated amount of 2% by weight usingMIBK as component (F), and 120 parts by weight (30 parts by weight interms of the solids) of a solution of a saturated thermoplasticelastomer {hydrogenation product of a styrene-butadiene copolymer;Tuftec H1043, styrene content: 67%, styrene-(ethylene-butylene)-styreneblock polymer (SEBS), manufactured by Asahi Kasei Chemicals Corporation}as component (E) preliminarily dissolved in toluene as component (G)were mixed together. Then, to the resultant mixture were added 50 partsby weight of methyl ethyl ketone (MEK) and 25 parts by weight of2,2-bis[4-(4-maleimidophenoxy)phenyl]propane (BMI-4000, manufactured byDAIWA KASEI CO., LTD.) as component (I), and the mixture was heated at70° C. for one hour to dissolve BMI-4000. Then, the resultant solutionwas cooled to 50° C. or lower, and the above-obtained polyphenyleneether-modified butadiene prepolymer and 5 parts by weight ofα,α′-bis(t-butylperoxy)diisopropylbenzene (PERBUTYL P, manufactured byNOF CORPORATION) as component (H) were added to the solution, followedby addition of MEK, to prepare a resin varnish (solids content: about40% by weight) in Preparation Example 5.

Preparation Example 6

(a) A polyphenylene ether-modified butadiene prepolymer was obtained insubstantially the same manner as in item (a) of Preparation Example 5except that, instead of N-phenylmaleimide, 15 parts by weight ofbis(4-maleimidophenyl)methane (BMI-1000, manufactured by DAIWA KASEICO., LTD.) was used. A conversion rate of BMI-1000 in the polyphenyleneether-modified butadiene prepolymer solution was measured by gelpermeation chromatography. As a result, it was found that the conversionrate was 32%.

(b) Subsequently, 171 parts by weight (120 parts by weight in terms ofthe solids) of a slurry (solids content: 70% by weight; solvent: MIBK)of SO-25R as component (D), which had preliminarily been subjected tosurface treatment with vinyltrimethoxysilane (KBM-1003, manufactured byShin-Etsu Chemical Co., Ltd.) in a treated amount of 2% by weight usingMIBK as component (F), and 120 parts by weight (30 parts by weight interms of the solids) of a solution of a saturated thermoplasticelastomer {hydrogenation product of a styrene-butadiene copolymer;Tuftec H1053, styrene content: 29%, styrene-(ethylene-butylene)-styreneblock polymer (SEBS), manufactured by Asahi Kasei Chemicals Corporation}as component (E) preliminarily dissolved in toluene as component (G)were mixed together. Then, to the resultant mixture were added 50 partsby weight of methyl ethyl ketone (MEK) and 25 parts by weight of2,2-bis[4-(4-maleimidophenoxy)phenyl]propane (BMI-4000, manufactured byDAIWA KASEI CO., LTD.) as component (I), and the mixture was heated at70° C. for one hour to dissolve BMI-4000. Then, the resultant solutionwas cooled to 50° C. or lower, and the above-obtained polyphenyleneether-modified butadiene prepolymer, 70 parts by weight ofethylenebis(pentabromophenyl) (SAYTEX 8010, manufactured by AlbemarleCorporation) as a flame retardant as component (J), and 5 parts byweight of α,α′-bis(t-butylperoxy)diisopropylbenzene (PERBUTYL P,manufactured by NOF CORPORATION) as component (H) were added to thesolution, followed by addition of methyl ethyl ketone (MEK), to preparea resin varnish (solids content: about 40% by weight) in PreparationExample 6.

Preparation Example 7

(a) A polyphenylene ether-modified butadiene prepolymer was obtained insubstantially the same manner as in item (a) of Preparation Example 5except that, instead of N-phenylmaleimide,bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (BMI-5100, manufacturedby DAIWA KASEI CO., LTD.) was used. A conversion rate of BMI-5100 in thepolyphenylene ether-modified butadiene prepolymer solution was measuredby gel permeation chromatography. As a result, it was found that theconversion rate was 35%.

(b) Subsequently, a resin varnish (solids content: about 40% by weight)in Preparation Example 7 was prepared in substantially the same manneras in Preparation Example 6 except that, instead of H1053 used ascomponent (E) in item (b) of Preparation Example 6, 20 parts by weightof an acid anhydride-modified elastomer obtained from a hydrogenationproduct of a styrene-butadiene copolymer (Tuftec M1913, styrene content:30%, manufactured by Asahi Kasei Chemicals Corporation) was used, andthat, instead of ethylenebis(pentabromophenyl) as a flame retardant ascomponent (J), 70 parts by weight of ethylenebistetrabromophthalimide(BT-93W, manufactured by Albemarle Corporation) was used.

Preparation Example 8

(a) A polyphenylene ether-modified butadiene prepolymer was obtained insubstantially the same manner as in Preparation Example 1 except that,instead of B-3000 as a chemically unmodified butadiene polymer ascomponent (B), Ricon 142 (manufactured by Sartomer Company; Mn: 3,900;1,2-vinyl structure: 55%) was used, and that, instead ofbis(4-maleimidophenyl)methane as component (C), 20 parts by weight ofdivinylbiphenyl (manufactured by Nippon Steel Chemical Co. Ltd.) wasused. A conversion rate of the divinylbiphenyl in the polyphenyleneether-modified butadiene prepolymer solution was measured by gelpermeation chromatography. As a result, it was found that the conversionrate was 30%.

(b) Subsequently, using the obtained solution, a resin varnish (solidscontent: about 40% by weight) in Preparation Example 8 was prepared insubstantially the same manner as in Preparation Example 7 except thatthe amount of the silica slurry used in item (b) of Preparation Example6 was changed to 143 parts by weight (100 parts by weight in terms ofthe solids), and that, instead of ethylenebis(pentabromophenyl), 70parts by weight of brominated polystyrene (PBS-64HW, manufactured byGreat Lakes Chemical Corporation) was used.

Preparation Example 9

(a) A polyphenylene ether-modified butadiene prepolymer was obtained inthe same manner as in item (a) of Preparation Example 1. A conversionrate of the bis(4-maleimidophenyl)methane (BMI-1000, manufactured byDAIWA KASEI CO., LTD.) in the polyphenylene ether-modified butadieneprepolymer solution was measured by gel permeation chromatography. As aresult, it was found that the conversion rate was 30%.

(b) Subsequently, 1,000 parts by weight (700 parts by weight in terms ofthe solids) of a slurry (solids content: 70% by weight; solvent: MIBK)of strontium titanate (SL 250, manufactured by FUJI TITANIUM INDUSTRYCO., LTD.; average particle size: 0.85 μm) as component (D), which hadpreliminarily been subjected to surface treatment with a titanatecoupling agent (PLENACT KR-TTS, manufactured by Ajinomoto Fine-TechnoCo., Ltd.) in a treated amount of 2% by weight in MIBK as component (F),and 120 parts by weight (30 parts by weight in terms of the solids) of asolution of a saturated thermoplastic elastomer {hydrogenation productof a styrene-butadiene copolymer; Tuftec H1043, styrene content: 67%,styrene-(ethylene-butylene)-styrene block polymer (SEBS), manufacturedby Asahi Kasei Chemicals Corporation} as component (E) preliminarilydissolved in toluene as component (G) were mixed together, and theabove-obtained polyphenylene ether-modified butadiene polymer solutionwas added to the resultant mixture, and 5 parts by weight ofα,α′-bis(t-butylperoxy)diisopropylbenzene (PERBUTYL P, manufactured byNOF CORPORATION) as component (H) was further added thereto, followed byaddition of methyl ethyl ketone (MEK), to prepare a resin varnish(solids content: about 40% by weight) in Preparation Example 9.

Comparative Preparation Example 1

(a) In a one-liter separable flask equipped with a thermometer, a refluxcondenser, and a stirrer were placed 200 parts by weight of toluene and50 parts by weight of polyphenylene ether (S202A, manufactured by AsahiKasei Chemicals Corporation; Mn: 16,000), and the solid component wasdissolved by stirring at a temperature of 90° C. inside the flask. Then,to the resultant solution was added 100 parts by weight of triallylisocyanurate (TAIC, manufactured by Nippon Kasei Chemical Co., Ltd.),and dissolution or uniform dispersion of the components was confirmed,followed by cooling to room temperature.

(b) Subsequently, 129 parts by weight (90 parts by weight in terms ofthe solids) of a slurry (solids content: 70% by weight; solvent: MIBK)of spherical silica (SO-25R, manufactured by Admatechs Co., Ltd.;average particle size: 0.5 μm) as component (D), which had preliminarilybeen subjected to surface treatment with vinyltrimethoxysilane(KBM-1003, manufactured by Shin-Etsu Chemical Co., Ltd.) in a treatedamount of 2% by weight using MIBK as component (F), and 120 parts byweight (30 parts by weight in terms of the solids) of a solution of asaturated thermoplastic elastomer {hydrogenation product of astyrene-butadiene copolymer; Tuftec H1043, styrene content: 67%,styrene-(ethylene-butylene)-styrene block polymer (SEBS), manufacturedby Asahi Kasei Chemicals Corporation} as component (E) preliminarilydissolved in toluene as component (G) were mixed together, and thesolution prepared in item (a) of Comparative Preparation Example 1 wasadded to the resultant mixture. Then, 5 parts by weight ofα,α′-bis(t-butylperoxy)diisopropylbenzene (PERBUTYL P, manufactured byNOF CORPORATION) as a reaction initiator was added to the mixture,followed by addition of methyl ethyl ketone (MEK), to prepare a resinvarnish (solids content: about 40% by weight) in Comparative PreparationExample 1.

Comparative Preparation Example 2

A resin varnish (solids content: about 40% by weight) in ComparativePreparation Example 2 was prepared in substantially the same manner asin Comparative Preparation Example 1 except that, instead of thetriallyl isocyanurate used in item (a) of Comparative PreparationExample 1, 100 parts by weight ofbis(3-ethyl-5-methyl-4-maleimidophenyl)methane (BMI-5100, manufacturedby DAIWA KASEI CO., LTD.) was used.

Comparative Preparation Example 3

A resin varnish (solids content: about 40% by weight) in ComparativePreparation Example 3 was prepared in substantially the same manner asin Comparative Preparation Example 1 except that, instead of triallylisocyanurate, 100 parts by weight of a chemically unmodified butadienepolymer (B-3000, manufactured by NIPPON SODA CO., LTD.; Mn: 3,000;1,2-vinyl structure: 90%) was used.

Comparative Preparation Example 4

A resin varnish (solids content: about 40% by weight) in ComparativePreparation Example 4 was prepared in substantially the same manner asin Comparative Preparation Example 1 except that the amount of thetriallyl isocyanurate (TAIC, manufactured by Nippon Kasei Chemical Co.,Ltd.) used in item (a) of Comparative Preparation Example 1 was changedto 50 parts by weight and 100 parts by weight of a chemically unmodifiedbutadiene polymer (B-3000, manufactured by NIPPON SODA CO., LTD.; Mn:3,000; 1,2-vinyl structure: 90%) was added, and that the amount of thespherical silica (SO-25R) was changed to 130% by weight.

Comparative Preparation Example 5

A resin varnish (solids content: about 40% by weight) in ComparativePreparation Example 5 was prepared in substantially the same manner asin Comparative Preparation Example 4 except that, instead of triallylisocyanurate, 30 parts by weight of bis(4-maleimidophenyl)methane(BMI-1000, manufactured by DAIWA KASEI CO., LTD.) was used, and that theamount of the spherical silica (SO-25R) was changed to 110% by weight.

Comparative Preparation Example 6

(a) In a one-liter separable flask equipped with a thermometer, a refluxcondenser, a vacuum evaporator, and a stirrer were placed 350 parts byweight of toluene and 50 parts by weight of polyphenylene ether (S202A,manufactured by Asahi Kasei Chemicals Corporation; Mn: 16,000), and thesolid component was dissolved by stirring at a temperature of 90° C.inside the flask. Then, to the resultant solution were added 100 partsby weight of glycol-modified 1,2-polybutadiene having a hydroxyl groupat the end thereof (G-3000, manufactured by NIPPON SODA CO., LTD.; Mn:3,000; 1,2-vinyl structure: 90%), 40 parts by weight ofbis(4-maleimidophenyl)methane (BMI-1000, manufactured by DAIWA KASEICO., LTD.), and methyl isobutyl ketone (MIBK) in such an amount that thesolids content (nonvolatile content) of the resultant solution became30% by weight. Dissolution or uniform dispersion of the components wasconfirmed. Then, while maintaining the temperature at 110° C., 0.5 partby weight of 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane (PERHEXATMH, manufactured by NOF CORPORATION) as a reaction initiator was addedto the resultant solution or dispersion, and a preliminary reaction waseffected for about 10 minutes while stirring. A conversion rate ofBMI-1000 in the preliminary reaction product was measured by gelpermeation chromatography. As a result, it was found that the conversionrate was 4%. (b) A resin varnish (solids content: about 40% by weight)in Comparative Preparation Example 6 was prepared in the same manner asin item (b) of Preparation Example 1.

Comparative Preparation Example 7

A preliminary reaction product was obtained in substantially the samemanner as in Comparative Preparation Example 6 except that, instead ofglycol-modified 1,2-polybutadiene, 100 parts by weight of carboxylicacid-modified 1,2-polybutadiene having a carboxyl group at the endthereof (C-1000, manufactured by NIPPON SODA CO., LTD.; Mn: 1,400;1,2-vinyl structure: 89%) was used. A conversion rate of BMI-1000 in thepreliminary reaction product was measured by gel permeationchromatography. As a result, it was found that the conversion rate was19%. Subsequently, using the obtained solution, a resin varnish (solidscontent: about 40% by weight) in Comparative Preparation Example 7 wasprepared in the same manner as in Comparative Preparation Example 6.

Comparative Preparation Example 8

A resin varnish (solids content: about 40% by weight) in ComparativePreparation Example 8 was prepared in substantially the same manner asin Preparation Example 1 except that, instead of the saturatedthermoplastic elastomer used as component (E) in item (b) of PreparationExample 1, an unsaturated elastomer {styrene-butadiene copolymer;Tufprene 125, styrene content: 40%; styrene-(ethylene-butylene)-styreneblock polymer (SBS), manufactured by Asahi Kasei Chemicals Corporation}was used.

Comparative Preparation Example 9

A resin varnish (solids content: about 40% by weight) in ComparativePreparation Example 9 was prepared in substantially the same manner asin Preparation Example 1 except that the solution of saturatedthermoplastic elastomer {hydrogenation product of a styrene-butadienecopolymer; Tuftec H1043, styrene content: 67%,styrene-(ethylene-butylene)-styrene block polymer (SEBS), manufacturedby Asahi Kasei Chemicals Corporation} as component (E) preliminarilydissolved in toluene as component (G) in item (b) of Preparation Example1 was not used.

Comparative Preparation Example 10

A resin varnish (solids content: about 40% by weight) in ComparativePreparation Example 10 was prepared in substantially the same manner asin Preparation Example 1 except that the slurry of spherical silica(SO-25R, manufactured by Admatechs Co., Ltd.; average particle size: 0.5μm) as component (D), which had preliminarily been subjected to surfacetreatment with vinyltrimethoxysilane (KBM-1003, manufactured byShin-Etsu Chemical Co., Ltd.) in a treated amount of 2% by weight usingMIBK as component (F), in item (b) of Preparation Example 1 was notused.

Comparative Preparation Example 11

(a) A preliminary reaction product of polybutadiene was obtained in thepresence of polyphenylene ether in the same manner as in item (a) ofPreparation Example 1. A conversion rate of BMI-1000 in the preliminaryreaction solution was measured by gel permeation chromatography. As aresult, it was found that the conversion rate was 24%.

(b) Subsequently, to the above-obtained solution was added 171 parts byweight (120 parts by weight in terms of the solids) of a slurry (solidscontent: 70% by weight; solvent: MIBK) of spherical silica (SO-25R,manufactured by Admatechs Co., Ltd.; average particle size: 0.5 μm) ascomponent (D), which had preliminarily been subjected to surfacetreatment with vinyltrimethoxysilane (KBM-1003, manufactured byShin-Etsu Chemical Co., Ltd.) in a treated amount of 2% by weight usingMIBK as component (F), and then 120 parts by weight (30 parts by weightin terms of the solids) of a solution of a saturated thermoplasticelastomer {hydrogenation product of a styrene-butadiene copolymer;Tuftec 141043, styrene content: 67%, styrene-(ethylene-butylene)-styreneblock polymer (SEBS), manufactured by Asahi Kasei Chemicals Corporation}as component (E) preliminarily dissolved in toluene as component (G) wasadded to the mixture. Then, 5 parts by weight ofα,α′-bis(t-butylperoxy)diisopropylbenzene (PERBUTYL P, manufactured byNOF CORPORATION) as component (H) was added to the mixture, followed byaddition of methyl ethyl ketone (MEK), to prepare a resin varnish(solids content: about 40% by weight) in Comparative Preparation Example11.

Comparative Preparation Example 12

(a) In a one-liter separable flask equipped with a thermometer, a refluxcondenser, a vacuum evaporator, and a stirrer were placed 350 parts byweight of toluene, 100 parts by weight of a chemically unmodifiedbutadiene polymer (B-3000, manufactured by NIPPON SODA CO., LTD.; Mn:3,000; 1,2-vinyl structure: 90%), and 40 parts by weight ofbis(4-maleimidophenyl)methane (BMI-1000, manufactured by DAIWA KASEICO., LTD.), and methyl isobutyl ketone (MIBK) as a solvent was addedthereto in such an amount that the solids content (nonvolatile content)of the resultant solution became 25% by weight, and the solid componentswere dissolved by stirring at a temperature of 110° C. inside the flask.Then, while maintaining the resultant solution at that temperature, 0.5part by weight of 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane(PERHEXA TMH, manufactured by NOF CORPORATION) as a reaction initiatorwas added to the solution, and a preliminary reaction was effected forabout 30 minutes while stirring to obtain a solution of the preliminaryreaction product of the chemically unmodified butadiene polymer andcrosslinking agent (bismaleimide). Then, to the obtained solution wasadded 50 parts by weight of polyphenylene ether (S202A, manufactured byAsahi Kasei Chemicals Corporation; Mn: 16,000) while stirring (thesolution was slightly opaque). A conversion rate of thebis(4-maleimidophenyl)methane in the solution was measured by gelpermeation chromatography. As a result, it was found that the conversionrate was 33%. Then, the temperature of the solution in the flask wasadjusted to 80° C., and the solution was then concentrated whilestirring so that the solids content of the solution became 45% byweight.

(b) A resin varnish (solids content: 40% by weight) in ComparativePreparation Example 12 was prepared in substantially the same manner asin Preparation Example 1 except that, instead of the polyphenyleneether-modified butadiene prepolymer prepared in item (a) of PreparationExample 1, the solution prepared in item (a) of Comparative PreparationExample 11 was used in item (b) of Preparation Example 1.

Comparative Preparation Example 13

A resin varnish (solids content: about 40% by weight) in ComparativePreparation Example 13 was prepared in substantially the same manner asin Preparation Example 5 except that the temperature at which thepolyphenylene ether-modified butadiene polymer was added was changedfrom 50° C. to 80° C.

The amounts of the raw materials used in the preparation of the resinvarnishes in Preparation Examples 1 to 9 and Comparative PreparationExamples 1 to 13 and the results of measurement of viscosity at 25° C.(using an E-type viscometer) of the prepared varnishes are summarizedand shown in Table 1.

TABLE 1 Preparation Example Comparative Preparation Example 1 2 3 4 5 67 8 9 1 2 3 Polyphenylene ether 50 50 50 50 50 50 50 50 50 50 50 50Butadiene homopolymer 100 100 100 100 100 100 100 100 100 100Glycol-modified polybutadiene Carboxylic acid-modified polybutadieneCrosslinking agent BMI-1000 40 15 40 BMI-2000 30 BMI-4000 35 25 25 25BMI-5100 40 15 100 IMILEX-P 15 Divinylbiphenyl 20 TAIC 100 Reactioninitiator PERHEXA TMH 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 PERBUTYL P 5 55 5 5 5 5 5 5 5 5 5 Saturated elastomer H1043 30 30 30 30 30 30 30 H105130 30 30 H1053 30 M1913 30 Unsaturated elastomer Tufprene 125 Inorganicfiller SO-25R 120 110 120 120 120 120 120 100 90 90 90 SL250 700 Silanecoupling agent KBM-1003 2 2 2 2 2 2 2 2 2 KBM-1403 2 KBM-573 2 KR-TTS 2Flame retardant SAYTEX801O 70 BT-93W 70 PBS-64HW 70 Varnish viscosity(mPa · s, 25° C., E-type) 92 95 80 78 83 110 120 125 102 65 72 160Comparative Preparation Example 4 5 6 7 8 9 10 11 12 13 Polyphenyleneether 50 50 50 50 50 50 50 50 50 50 Butadiene homopolymer 100 100 100100 100 100 100 100 Glycol-modified polybutadiene 100 Carboxylicacid-modified polybutadiene 100 Crosslinking agent BMI-1000 30 40 40 4040 40 40 40 BMI-2000 BMI-4000 25 BMI-5100 IMILEX-P 15 DivinylbiphenylTAIC 50 Reaction initiator PERHEXA TMH 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5PERBUTYL P 5 5 5 5 5 5 5 5 5 5 Saturated elastomer H1043 30 30 30 30 3030 30 H1051 30 H1053 M1913 Unsaturated elastomer Tufprene 125 30Inorganic filler SO-25R 130 110 120 120 120 120 120 120 120 SL250 Silanecoupling agent KBM-1003 2 2 2 2 2 2 2 2 2 KBM-1403 KBM-573 KR-TTS Flameretardant SAYTEX801O BT-93W PBS-64HW Varnish viscosity (mPa · s, 25° C.,E-type) 140 121 115 134 84 65 210 85 88 78 (The amount of each materialis indicated by part or parts by weight, except for the amount ofcoupling agent, which is an amount (wt %) used in the treatment, basedon the weight of the inorganic filler.)

The abbreviations shown in the table have the following meanings.

BMI: Bismaleimide compound

IMILEX-P: N-Phenylmaleimide

TAIC: Triallyl isocyanuratePERHEXA TMH: 1,1-Bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane

PERBUTYL P: α,α′-Bis(t-butylperoxy)diisopropylbenzene

-   H1043: Hydrogenation product of a styrene-butadiene copolymer-   H1051: Hydrogenation product of a styrene-butadiene copolymer-   H1053: Hydrogenation product of a styrene-butadiene copolymer-   M1913: Acid anhydride-modified elastomer obtained from a    hydrogenation product of a styrene-butadiene copolymer-   SO-25R: Spherical silica-   SL 250: Strontium titanate-   KBM-1003: Vinyltrimethoxysilane-   KBM-1403: p-Styryltrimethoxysilane-   KBM-573: N-Phenyl-3-aminopropyltrimethoxysilane-   KR-TTS: Titanate coupling agent-   SAYTEX 8010: Ethylenebis(pentabromophenyl)-   BT-93W: Ethylenebistetrabromophthalimide-   PBS-64HW: Brominated polystyrene

Fabrication of Prepreg

Glass cloth having a thickness of 0.1 mm (E glass, manufactured by NittoBoseki Co., Ltd.) was impregnated with each of the resin varnishesobtained in Preparation Examples 1 to 9 and Comparative PreparationExamples 1 to 13, and then dried by heating at 100° C. for 5 minutes toform prepregs in Fabrication Examples 1 to 9 and Comparative FabricationExamples 1 to 13, each having a resin content of 50% by weight (54% byweight in the system containing the inorganic filler). The prepregsusing the resin varnishes in Preparation Examples 1 to 9 correspond toFabrication Examples 1 to 9, respectively, and the prepregs using theresin varnishes in Comparative Preparation Examples 1 to 13 correspondto Comparative Fabrication Examples 1 to 13, respectively.

Evaluation of Prepreg

With respect to each of the prepregs in Fabrication Examples 1 to 9 andComparative Fabrication Examples 1 to 13, appearance and tackiness wereevaluated. The results of the evaluation are shown in Table 2. Theappearance of the prepreg was visually evaluated, and a prepreg havingpoor surface smoothness such that irregularities, streaks, or the likewere caused in the surface of the prepreg was rated “X”, and a prepreghaving a smooth surface such that no irregularities, streaks, or thelike were caused in the surface of the prepreg was rated “◯”. Withrespect to the evaluation of tackiness of the prepreg, a prepreg havinga surface which was sticky (tacky) at 25° C. was rated “X”, and aprepreg other than such a prepreg was rated “◯”.

Production of Double-Sided Copper-Clad Laminate

With respect to each of the prepregs in Fabrication Examples 1 to 9 andComparative Fabrication Examples 1 to 13, four sheets of the prepregwere stacked on one another, and on the upper and lower surfaces of theresultant stacked article were respectively disposed low-profile copperfoils each having a thickness of 18 μm (F3-WS, manufactured by THEFURUKAWA ELECTRIC CO., LTD.; M-side Rz: 3 μm) so that the M side of eachcopper foil was in contact with the surface of the stacked article, andthey were together pressed while heating under pressing conditions at200° C. under 2.9 MPa for 70 minutes to produce a double-sidedcopper-clad laminate (thickness: 0.5 mm). Further, with respect to eachof the prepregs in Fabrication Example 1 and Comparative FabricationExample 1, a double-sided copper-clad laminate using a general copperfoil having a thickness of 18 μm (GTS, manufactured by THE FURUKAWAELECTRIC CO., LTD.; M-side Rz: 8 μm) was produced under the samepressing conditions as those in the Examples using a low-profile copperfoil. The combinations of the prepregs in Fabrication Examples 1 to 9and Comparative Fabrication Examples 1 to 13 and the copper foils usedin the copper-clad laminates in Examples 1 to 10 and ComparativeExamples 1 to 14 are shown in Table 2.

Evaluation of Properties of Double-Sided Copper-Clad Laminate

With respect to each of the copper-clad laminates in Examples 1 to 10and Comparative Examples 1 to 14, transmission loss, dielectricproperties, copper foil peeling strength, resistance to soldering heat,thermal expansion coefficient, and Tg were evaluated. The results of theevaluation are shown in Table 2. The processes for evaluation of theproperties of a copper-clad laminate are as follows.

Measurement of Transmission Loss and Dielectric Properties

A transmission loss of a copper-clad laminate was measured by atriplate-line resonator method using a vector-type network analyzer.Conditions for the measurement were as follows: line width: 0.6 mm;insulating layer distance between the upper and lower ground conductors:about 1.0 mm; line length: 200 mm; characteristic impedance: about 50Ω;frequency: 3 GHz; and measurement temperature: 25° C. From the obtainedtransmission loss, dielectric properties (relative permittivity anddielectric loss tangent) at 3 GHz were determined by making acalculation. Further, dielectric properties (relative permittivity anddielectric loss tangent) were measured with respect to the copper-cladlaminate which had been kept in a machine for pressure cooker test (PCT)(conditions: 121° C., 2.2 atm.) for 5 hours. Conditions for themeasurement were the same as those for the above measurement in theordinary state.

Measurement of Copper Foil Peeling Strength

A copper foil peeling strength of a copper-clad laminate was measured inaccordance with JIS-C-6481 test standard for copper-clad laminate.

Evaluation of Resistance to Soldering Heat of Copper-Clad Laminate

The copper foil on the both sides or one side of the copper-cladlaminate cut into 50 mm square was etched, and the resultant laminate,which was in the ordinary state, or which had been kept in a machine forpressure cooker test (PCT) (conditions: 121° C., 2.2 atm.) for apredetermined time (1, 3, or 5 hours), was immersed in molten solder at288° C. for 20 seconds, and the appearance of the resultant copper-cladlaminate (three sheets) was visually evaluated. The figures shown in thetable below mean, among the three sheets of copper-clad laminate whichhad been immersed in the solder, the number of the sheet(s) ofcopper-clad laminate in which the occurrence of blister or measlingwithin the substrate (within the insulating layer) and between thesubstrate and the copper foil was not recognized.

Measurement of Thermal Expansion Coefficient and Tg of Copper-CladLaminate

The copper foils on the both sides of the copper-clad laminate wereetched, and a thermal expansion coefficient (in the thicknesswisedirection, at 30 to 130° C.) and Tg of the copper-clad laminate cut into5 mm square were measured by a TMA.

TABLE 2 Dielectric loss Relative permittivity (3 GHz) tangent (3 GHz)Prepreg properties In ordinary After 5 h In ordinary After 5 h Resinvarnish Prepreg Copper foil Appearance Tackiness state PCT state PCTExample 1 Preparation Fabrication Low-profile foil ∘ ∘ 3.38 3.48 0.00260.0047 Example 1 Example 1 Example 2 Preparation Fabrication Generalfoil ∘ ∘ 3.38 3.48 0.0026 0.0047 Example 1 Example 1 Example 3Preparation Fabrication Low-profile foil ∘ ∘ 3.41 3.52 0.0027 0.0048Example 2 Example 2 Example 4 Preparation Fabrication Low-profile foil ∘∘ 3.37 3.46 0.0026 0.0047 Example 3 Example 3 Example 5 PreparationFabrication Low-profile foil ∘ ∘ 3.37 3.44 0.0026 0.0045 Example 4Example 4 Example 6 Preparation Fabrication Low-profile foil ∘ ∘ 3.373.45 0.0026 0.0045 Example 5 Example 5 Example 7 Preparation FabricationLow-profile foil ∘ ∘ 3.41 3.50 0.0026 0.0046 Example 6 Example 6 Example8 Preparation Fabrication Low-profile foil ∘ ∘ 3.43 3.49 0.0025 0.0045Example 7 Example 7 Example 9 Preparation Fabrication Low-profile foil ∘∘ 3.44 3.52 0.0026 0.0046 Example 8 Example 8 Example 10 PreparationFabrication Low-profile foil ∘ ∘ 9.40 9.52 0.0025 0.0045 Example 9Example 9 Comparative Comparative Comparative Low-profile foil ∘ ∘ 3.884.06 0.0050 0.0101 Example 1 Preparation Fabrication Example 1 Example 1Comparative Comparative Comparative General foil ∘ ∘ 3.88 4.06 0.00500.0101 Example 2 Preparation Fabrication Example 1 Example 1 ComparativeComparative Comparative Low-profile foil ∘ ∘ 4.08 4.27 0.0148 0.0208Example 3 Preparation Fabrication Example 2 Example 2 ComparativeComparative Comparative Low-profile foil x x 3.45 3.55 0.0032 0.0052Example 4 Preparation Fabrication Example 3 Example 3 ComparativeComparative Comparative Low-profile foil x x 3.60 3.71 0.0040 0.0080Example 5 Preparation Fabrication Example 4 Example 4 ComparativeComparative Comparative Low-profile foil x x 3.41 3.51 0.0032 0.0052Example 6 Preparation Fabrication Example 5 Example 5 ComparativeComparative Comparative Low-profile foil x ∘ 3.90 4.06 0.0136 0.0196Example 7 Preparation Fabrication Example 6 Example 6 ComparativeComparative Comparative Low-profile foil ∘ ∘ 3.95 4.09 0.0147 0.0206Example 8 Preparation Fabrication Example 7 Example 7 ComparativeComparative Comparative Low-profile foil ∘ ∘ 3.40 3.50 0.0028 0.0048Example 9 Preparation Fabrication Example 8 Example 8 ComparativeComparative Comparative Low-profile foil ∘ ∘ 3.41 3.51 0.0028 0.0049Example 10 Preparation Fabrication Example 9 Example 9 ComparativeComparative Comparative Low-profile foil ∘ ∘ 3.21 3.30 0.0028 0.0048Example 11 Preparation Fabrication Example 10 Example 10 ComparativeComparative Comparative Low-profile foil ∘ ∘ 3.40 3.51 0.0027 0.0052Example 12 Preparation Fabrication Example 11 Example 11 ComparativeComparative Comparative Low-profile foil x x 3.42 3.53 0.0029 0.0052Example 13 Preparation Fabrication Example 12 Example 12 ComparativeComparative Comparative Low-profile foil ∘ ∘ 3.38 3.45 0.0026 0.0048Example 14 Preparation Fabrication Example 13 Example 13 Resistance tosoldering heat Thermal Transmission loss (In ordinary state or after PCTtreatment) expansion (In ordinary state) Peeling strength In ordinary Tgcoefficient (dB/m, 3 GHz) (kN/m) state After 1 h After 3 h After 5 h (°C.) (ppm/° C.) Example 1 3.36 0.85 3 3 3 3 177 53 Example 2 4.02 1.17 33 3 3 177 53 Example 3 3.42 0.87 3 3 3 3 180 52 Example 4 3.34 0.97 3 33 3 174 54 Example 5 3.35 0.86 3 3 3 3 178 49 Example 6 3.35 0.96 3 3 33 174 55 Example 7 3.38 0.98 3 3 3 3 175 54 Example 8 3.32 0.91 3 3 3 3177 50 Example 9 3.40 0.91 3 3 3 3 172 59 Example 10 5.66 0.82 3 3 3 3178 59 Comparative 4.95 0.57 3 3 3 1 174 59 Example 1 Comparative 5.660.93 3 3 3 3 174 59 Example 2 Comparative 10.44 0.74 3 3 3 2 203 48Example 3 Comparative 3.78 0.49 3 2 0 0 156 82 Example 4 Comparative4.24 0.56 3 3 1 0 165 75 Example 5 Comparative 3.76 0.56 3 1 0 0 168 69Example 6 Comparative 9.63 0.74 3 3 2 0 164 78 Example 7 Comparative10.19 0.83 3 2 1 0 160 73 Example 8 Comparative 3.47 0.84 3 3 3 3 143 52Example 9 Comparative 3.48 0.83 3 3 3 3 177 52 Example 10 Comparative3.41 0.85 3 3 3 3 177 61 Example 11 Comparative 3.42 0.85 3 3 3 3 177 53Example 12 Comparative 3.48 0.55 3 3 0 0 169 59 Example 13 Comparative3.35 0.93 3 3 3 0 173 56 Example 14

As apparent from Table 2, in each of Examples 1 to 10 in which the resinvarnish of the present invention was used, the prepreg properties areexcellent such that the appearance is free of irregularities, streaks,and the like and hence is smooth and further free of tackiness (surfaceslickness). In each of the Examples except Example 10 which was intendedfor the increase of the permittivity, the laminate properties areexcellent such that the relative permittivity is 3.44 or less and thedielectric loss tangent is 0.0027 or less. The resistance to solderingheat is excellent such that the occurrence of lifting or measling is notrecognized in any of the three samples for measurement. The thermalexpansion properties are excellent such that the thermal expansioncoefficient is 59 ppm/° C. or less.

With respect to the transmission loss and peeling strength, in Example 2in which the resin varnish of the present invention and a general foilwere used, the transmission loss was remarkably excellent, with a valueof 4.02, and the peeling strength was also excellent with a value of1.17 kN/m, as compared to those in Comparative Example 2 in which ageneral foil was used similarly.

The copper-clad laminate in each of the Examples in which the resinvarnish of the present invention and a low-profile foil were used,except Example 10 which was intended for the increase of thepermittivity, the transmission loss is as especially excellent as 3.42or less, and the peeling strength is as high as 0.82 kN/m or more eventhough the low-profile foil is used. From this, it is apparent that theresin varnish of the present invention can very advantageously achieveboth the reduction of transmission loss and the improvement of peelingstrength.

Comparative Examples 1 and 2 are of a system in which an inorganicfiller and a saturated elastomer are used in combination in a resinsystem comprising a polyphenylene ether and triallyl isocyanurate, andComparative Example 1 corresponds to Patent documents 4 and 5 using alow-profile foil instead of the general foil and Comparative Example 2using a general foil corresponds to Patent documents 4 and 5. In thissystem, the prepreg properties and thermal expansion coefficient areexcellent, but the relative permittivity, dielectric loss tangent, andtransmission loss are poor. When using a low-profile foil, the peelingstrength is poor, and further the resistance to soldering heat is poor,and thus the performance is collectively unsatisfactory.

Comparative Example 3 is of a system in which an inorganic filler and asaturated elastomer are used in combination in a resin system comprisinga polyphenylene ether and a bismaleimide compound, and corresponds toPatent document 2 using a low-profile foil instead of the general foil.In this system, the prepreg properties and thermal expansion coefficientare excellent, but the relative permittivity, dielectric loss tangent,and transmission loss are poor, and the peeling strength is low andfurther the resistance to soldering heat is poor, and thus theperformance is collectively unsatisfactory.

Comparative Example 4 is of a system in which an inorganic filler and asaturated elastomer are used in combination in a conventional resinsystem comprising a polyphenylene ether and a butadiene homopolymerwhich are not compatibilized with each other, and corresponds to Patentdocuments 6 and 7 using a low-profile foil instead of the general foil.In this system, the relative permittivity, dielectric loss tangent, andtransmission loss are excellent, but the prepreg properties, peelingstrength, resistance to soldering heat, and thermal expansioncoefficient are poor, and thus the performance is collectivelyunsatisfactory. This system has suffered macro phase separation, andtherefore can be easily distinguished by visual observation from asample using the compatibilized composition in the present invention.

Comparative Example 5 is of a system in which an inorganic filler and asaturated elastomer are used in combination in a conventional resinsystem comprising a polyphenylene ether, a butadiene homopolymer, andtriallyl isocyanurate which are not compatibilized with one another. Inthis system, the relative permittivity, dielectric loss tangent, andtransmission loss are unsatisfactory, and the prepreg properties,peeling strength, resistance to soldering heat, and thermal expansioncoefficient are poor, and thus the performance is collectively poor.This system has suffered macro phase separation, and therefore can beeasily distinguished by visual observation from a sample using thecompatibilized composition in the present invention.

Comparative Example 6 is of a system in which an inorganic filler and asaturated elastomer are used in combination in a resin system comprisinga polyphenylene ether, a butadiene homopolymer, and a maleimidecompound, and corresponds to the resin composition comprising the samecomponents as those in the present invention, which are notcompatibilized with one another. In this system, the relativepermittivity, dielectric loss tangent, and transmission loss areunsatisfactory, and the prepreg properties, peeling strength, resistanceto soldering heat, and thermal expansion coefficient are poor, and thusthe performance is collectively poor. This system has suffered macrophase separation, and therefore can be easily distinguished by visualobservation from a sample using the compatibilized composition in thepresent invention.

Comparative Example 7 is of a system in which an inorganic filler and asaturated elastomer are used in combination in a conventional resinsystem comprising a polyphenylene ether, glycol-modified polybutadiene,and a maleimide compound which are not compatibilized with one another,and corresponds to Patent document 8 using a low-profile foil instead ofthe general foil. In this system, the relative permittivity, dielectricloss tangent, and transmission loss are poor, and further the peelingstrength, resistance to soldering heat, and thermal expansioncoefficient are poor, and thus the performance is collectively poor.This system has suffered macro phase separation, and therefore can beeasily distinguished by visual observation from a sample using thecompatibilized composition in the present invention.

Comparative Example 8 is of a system in which an inorganic filler and asaturated elastomer are used in combination in a resin system comprisinga polyphenylene ether, carboxylic acid-modified polybutadiene, and amaleimide compound, and corresponds to Patent document 8 using alow-profile foil instead of the general foil. In this system, therelative permittivity, dielectric loss tangent, and transmission lossare poor, and further the peeling strength, resistance to solderingheat, and thermal expansion coefficient are poor, and thus theperformance is collectively poor.

Comparative Example 9 is of a system in which an inorganic filler and anunsaturated elastomer are used in combination in a resin systemcomprising a polyphenylene ether, a butadiene homopolymer, and amaleimide compound. In this system, the transmission loss and Tg arepoor, as compared to those in Example 1 of the present invention.

Comparative Example 10 corresponds to substantially the same system asin Example 1 except that the saturated thermoplastic elastomer is notused. In this system, the prepreg properties, peeling strength,resistance to soldering heat, thermal expansion coefficient, and Tg areexcellent, but the relative permittivity, dielectric loss tangent, andtransmission loss are slightly poor, as compared to those in Example 1.

Comparative Example 11 corresponds to substantially the same system asin Example 1 except that the inorganic filler is not used. In thissystem, the prepreg properties, relative permittivity, peeling strength,resistance to soldering heat, and Tg are excellent, but the dielectricloss tangent, transmission loss, and thermal expansion coefficient areslightly poor, as compared to those in Example 1.

Comparative Example 12 corresponds to substantially the same system asin Example 1 except that the process for mixing together the inorganicfiller and thermoplastic elastomer is changed. In this system, theprepreg properties, peeling strength, resistance to soldering heat, andTg are excellent, but the relative permittivity, dielectric losstangent, transmission loss, and moisture absorption dependency of thedielectric properties are slightly poor, as compared to those in Example1.

Comparative Example 13 is of a system in which a butadiene homopolymerand a bismaleimide compound are preliminarily reacted to obtain aprepolymer, and then a polyphenylene ether is added to the obtainedprepolymer, wherein the prepolymer obtained from the butadienehomopolymer and bismaleimide compound and the polyphenylene ether arenot compatibilized with each other. In this system, the relativepermittivity, dielectric loss tangent, and transmission loss areslightly unsatisfactory, and the prepreg properties, peeling strength,resistance to soldering heat, and thermal expansion coefficient areslightly poor, as compared to those in Example 1.

Comparative Example 14 is of a system in which the polyphenyleneether-modified butadiene polymer is added at 80° C., and, in thissystem, the dielectric loss tangent after moisture absorption andresistance to soldering heat are slightly poor, as compared to those inExample 5 in which the polyphenylene ether-modified butadiene polymer isadded at 50° C.

Comparison is made between the low-profile foil and the general foilwhen the same resin varnish and prepreg are used. As apparent fromExamples 1 and 2 or Comparative Examples 1 and 2, the low-profile foilis excellent in the transmission loss. On the other hand, thelow-profile foil is poor in the metallic foil peeling strength (peelingstrength). Particularly, in Comparative Example 1 in which a low-profilefoil is used for the conventional resin composition, the transmissionloss is 4.95 dB/m (low-profile foil), which is slightly improved, ascompared to the transmission loss (5.66 dB/m) of the general foil. Onthe other hand, the peeling strength for the low-profile foil is 0.57kN/m, which is poor, as compared to the peeling strength (0.93 kN/m) forthe general foil, and which is practically unsatisfactory. These resultssubstantiate the fact that, as mentioned above in connection with theproblems accompanying the prior art, the low-profile foil is moreeffective in reducing the transmission loss than a general foil, but,conversely, a general foil is more effective in improving the metallicfoil peeling strength than the low-profile foil, and therefore it hasbeen difficult to achieve both the reduction of transmission loss andthe required metallic foil peeling strength.

INDUSTRIAL APPLICABILITY

In the resin composition in the present invention, the thermosettingresin composition comprising a combination of the compatibilized uncuredsemi-IPN composite, inorganic filler, and saturated thermoplasticelastomer is advantageous not only in that, when used in a printedcircuit board, it exhibits excellent dielectric properties and reducesthe transmission loss in a high frequency band, namely, it exhibitsexcellent electrical properties and excellent heat resistance aftermoisture absorption as well as low thermal expansion properties, butalso in that it has metallic foil peeling strength satisfactorilyimproved. When an attempt is made to achieve both the reduction ofdielectric loss by the improvement of the dielectric properties and thereduction of conductor loss by the use of a metallic foil having smallsurface roughness, the resin varnish, prepreg, and metal-clad laminateof the present invention can satisfactorily reduce the transmission lossin a high frequency band, and therefore can advantageously be used inthe production of a printed circuit board used in the high frequencyfield.

The present invention is advantageously used in the application of amember or part for printed circuit board for use in various electric orelectronic devices, e.g., mobile communication devices using highfrequency signals in a high frequency band, for example, having afrequency of 1 GHz or more and devices for their base stations,network-associated electronic devices, such as a server and a router,and large-size computers.

1. A thermosetting resin varnish comprising: a thermosetting resincomposition of an uncured semi-IPN composite having compatibilized withone another (A) a polyphenylene ether, (B) a butadiene polymer whichcontains in the molecule thereof 40% or more of a 1,2-butadiene unithaving a 1,2-vinyl group in the side chain thereof, and which is notchemically modified, and (C) a crosslinking agent; (D) an inorganicfiller; and (E) a saturated thermoplastic elastomer.
 2. Thethermosetting resin varnish according to claim 1, which has a viscosityof 10 to 300 mPa·s at 25° C.
 3. A resin varnish for printed circuitboard, obtained by using the process for producing a thermosetting resinvarnish according to claim
 1. 4. A prepreg obtained by impregnating asubstrate with the thermosetting resin varnish according to claim 1, andthen drying the resultant substrate at 60 to 200° C.
 5. A metal-cladlaminate obtained by stacking one or more sheets of the prepregaccording to claim 4 on one another to prepare a stacked prepreg,disposing a metallic foil on one side or both sides of the stackedprepreg, and pressing them together while heating.
 6. A prepreg obtainedby impregnating a substrate with the resin varnish for printed circuitboard according to claim 3, and then drying the resultant substrate at60 to 200° C.
 7. A metal-clad laminate obtained by stacking one or moresheets of the prepreg according to claim 6 on one another to prepare astacked prepreg, disposing a metallic foil on one side or both sides ofthe stacked prepreg, and pressing them together while heating.